GIFT   OF 
Dean  Frank  H.    Probert 


RECENT  CYANIDE 
PRACTICE 


EDITED 
BY 

T.  A,  RICKARD 


FIRST  EDITION 


1907 

PUBLISHED   BY   THE 

MINING  AND   SCIENTIFIC  PRESS 
SAN  FRANCISCO 


mm 

DEPl. 


GIFT  Off 

DEAN  FRANK  H  ROBERT 

DINING  DEPL 

COPYRIGHT,  1907 

BY 
MINING  AND  SCIENTIFIC  PRESS 


PREFACE. 

This  book  gives,  in  convenient  form,  a  compilation  of  the 
series  of  articles  on  cyanidation  as  they  have  appeared  in  the 
pages  of  the  MINING  AND  SCIENTIFIC  PRESS  between  January, 
1906,  and  October,  1907.  The  contributors  are  the  leaders  in 
this  branch  of  metallurgy  and  they  describe  the  practice  in 
mills  all  over  the  world,  from  Nevada  to  New  Zealand,  and 
from  the  Transvaal  to  Korea. 

T.  A.  RICKARD, 

Editor. 

SAN  FRANCISCO,  October  12,  1907. 


TABLE    OF    CONTENTS 


Page 

Cyanide  as  a  Factor  in  Gold  Production G.  T.  Beilby  9 

The  Cyanide  Process  at  Guanajuato Francis  J.  Hobson  12 

Fine  Grinding Godfrey  Doveton  16 

Filter-Press  Practice  in  Western  Australia A.  B.  Wallace  18 

Cyanidation  of  Concentrate Francis  J.  Hobson  22 

Fine  Grinding Francis  L.  Bosqui  25 

Fine  Grinding Editorial  29 

Fine  Grinding M.  P.  Boss  31 

Milling   v.  Smelting   in    the    Treatment   of   Tonopah-Goldfield    Ores— 

Francis  L.  Bosqui  33 

Re-Grinding Editorial  37 

Iron  v.  Wood  for  Cyanide  Leaching  Vats Francis  L.  Bosqui  39 

The  Assay  of  Cyanide  Solutions William  Magenau  42 

The  Assay  of  Cyanide  Solutions. ,( Norman  C.  Stines  50 

The  Treatment  of  Desert  Ores Francis  L.  Bosqui  51 

Notes  on  Tube-Mills  at  El  Oro,  Mexico Charles  Butters  55 

Metallurgical  Development  on  the  Rand.  .(7.  A.  Denny  and//.  S.  Denny  59 

The  Treatment  of  Desert  Ores Bertram  Hunt  65 

Progress  of  Cyanidation Editorial  67 

Tube-Mill  Lining 69 

Crushing  and  Grinding  Practice  at  Kalgoorlie Alfred  James  73 

Pans  v.  Tubes D.  P.  Mitchell  78 

Zinc  Dust  v.  Shaving Cyanide  Man  80 

The  Treatment  of  Desert  Ores Lochiel  M.  King  82 

Cyanide  Notes E.  A,  H.  Tays  86 

Copper  and  Cyanide  Solutions R.  B.  S  90 

Cyanide  Practice  with  the  Moore  Filter — I R.  Oilman  Brown  92 

Cyanide  Practice  with  the  Moore  Filter — II R.  Gilman  Brown  98 

Tube-Milling  in  Korea . A.  E.  Drucker  110 

Cyanide  Practice  at  El  Oro— I T.  A.  Richard  114 

Cyanide  Poisoning 123 

Cyanide  Practice  at  El  Oro— II T.  A.  Richard  125 

Copper  in  Cyanide  Solutions C,  A.  Arents  132 

Zinc-Dust  Precipitation Mark  R.  Lamb  134 

Ore  Treatment  at  the  Combination  Mine,  Goldfield,  Nevada — 

Francis  L.  Bosqui  136 

Filter  Machines //.  W.  Gartrell  153 

What  is  Slime? M.  P.  Boss  154 

The  Action  of  Oxygen  in  Cyanide  Solutions H.  Julian  155 

Some  Tailing  Samplers R.  Gilman  Broivn  157 


6  TABLE  OF   CONTENTS 

Page 

Copper  in  Cyanide  Solutions r ...  ...E.  D.  Chandler  161 

Tube-Mill  Lining 5.  D.  McMiken  162 

Comparative  Tests  Between  Coke  and  Crude  Oil  for  Melting  Precipitate 

E.  M.  Hamilton  164 

Tube-Mill  Lining ... A  .E.  Drucker  166 

A  Simple  Solution  Meter E.  H.  Nutter  170 

Progress  in  Cyanidation Editorial  172 

Cyanide  Practice  with  the  Moore  Filter. .Edward  H.  Nutter  174 

Recent  Improvements  in  the  Cyanide  Process. ;  .  .  .  .F.  L.  Bosqui  181 

Cyanide  Practice  at  Kalgoorlie H.  T.  Brett   189 

Cyanide  Practice  at  Kalgoorlie Alfred  James  195 

Progress  in  Cyanidation  During  1906 Alfred  James  197 

Tube-Mill  Lining Walter  W.  Bradley  207 

Cyanide  Clean-up James  E.  Thomas  210 

The  Moore  and  Butters  Filters Mark  R.  Lamb  213 

Siphon  Device  for  Removing  Floating  Material .Edward  S.  Wiard  215 

The  Butters  Filter Mark  R.  Lamb  218 

The  Ridgway  Filter. 221 

The  Butters  Filter. Edward  H.  Nutter  225 

Cyanidation  at  Copala,  Mexico Laurence  N.  B.  Bullock  231 

The  Butters  Filter E.  S.  Pettis  235 

Tube-Mill  Lining H.  P.  Barry  239 

Assay  of  Cyanide  Solutions H.  W.  Gendar  240 

The  Butters  Filter Y  .  Mark  R.  Lamb  241 

Pans  v.  Tube-Mills ' Robert  Clarke  245 

The  Treatment  of  Desert  Ores Bertram  Hunt  247 

Slime  Filters /.  R.  Blake  249 

Assay  of  Cyanide  Solutions Douglas  Muir  251 

Slime  Filtering Old  Subscriber  252 

Cyanide  Practice  at  the  Waihi E.  G.  Banks  253 

Metallurgical  Development  at  Guanajuato T.  A.  Rickard  254 

Treatment  of  Matte  from  the  Cyanide  Mill A.  E.  Drucker  260 

Cyanide  Practice  at  Copala L.  McN.  B.  Bullock  265 

Assay  of  Cyanide  Solutions Augustus  Mac  Donald  267 

The  Filtration  of  Slime  by  the  Butters  Method E.  M.  Hamilton  269 

Old  and  New  Methods  at  Guanajuato,  Mexico T.  A.  Rickard  296 

Cyanide  Practice  at  the  Homestake  Mills F.  L.  Bosqui  302 

Vacuum  Slime  Filters A.  G.  Kirby  312 

Conveying  Tailing  Through  Pipe C.  W.  Van  Law  320 

Cyanidation  in  the  Transvaal Another  Correspondent  322 

Cyanidation  in  the  Transvaal Denny  Bros.    325 

Tube-Mills  at  Guanajuato C.  W.  Van  Law  329 

Conveying  Tailing  in  Launders G.  A.  Overstrom  331 

Conveying  Tailing  in  Launders C.  W.  Van  Law  331 


CYANIDE  AS  A  FACTOR  IN  GOLD  PRODUCTION 

(January  6,  1906) 

In  his  presidential  address  before  the  chemical  section  of 
the. British  Association,  G.  T.  Beilby  said  : 

From  the  early  beginnings  of  civilization  gold  has  been 
highly  prized  and  eagerly  sought  after.  Human  life  has  been 
freely  sacrificed  in  its  acquirement  from  natural  sources,  as  well 
as  in  its  forcible  seizure  from  those  who  already  possessed  it. 
The  'Age  of  Gold'  was  not  necessarily  the  'Golden  Age,'  for 
the  noble  metal,  in  its  unique  and  barbaric  splendor,  has  symbol- 
ized much  that  has  been  unworthy  in  national  and  individual 
aims  and  ideals.  With  the  advent  of  the  industrial  age  gold  was 
destined  to  take  a  new  place  in  the  world's  history  as  the  great 
medium  of  exchange,  the  great  promotor  of  industry  and  com- 
merce. While  individual  gain  still  remained  the  propelling  power 
toward  its  discovery  and  acquisition,  every  fresh  discovery  led 
directly  or  indirectly  to  the  freer  interchange  of  the  products  of 
industry,  and  thus  reacted  favorably  on  the  industrial  and  social 
conditions  of  the  time.  So  long  as  the  chief  supplies  of  gold 
were  obtained  from  alluvial  deposits  by  the  simple  process  of 
washing,  the  winning  of  gold  almost  necessarily  continued  to  be 
pursued  by  individuals,  or  by  small  groups  of  workers,  who  were 
mainly  attracted  by  the  highly  speculative  nature  of  the  occupa- 
tion. These  workers  endured  the  greatest  hardships  and  ran  the 
most  serious  personal  risks,  drawn  on  from  day  to  day  by  the 
hope  that  some  special  stroke  of  good  fortune  would  be  theirs. 
This  condition  prevailed  also  in  fields  in  which  the  reef  gold 
occurred  near  the  surface,  where  it  was  easily  accessible  without 
costly  mining  appliances,  and  where  the  precious  metal  was 
loosely  associated  with  a  weathered  matrix.  These  free-milling 
ores  could  be  readily  handled  by  crushing  and  amalgamation 
with  mercury,  so  that  here  also  no  elaborate  organization  and  no 
great  expenditure  of  capital  were  necessary.  A  third  stage 
was  reached  when  the  more  easily-worked  deposits  above  the 
water-line  had  been  worked  out.  Not  only  were  more  costly 
appliances  and  more  elaborately  organized  efforts  required  to 
bring  the  ore  to  the  surface,  but  the  ore,  when  obtained,  contained 


10  RECENT  CYANIDE  PRACTICE. 

less  of  its  gold  in  the  easily  recovered,  and  more  in  the  refractory 
or  combined  form.  The  problem  of  recovery  had  now  to  be  at- 
tacked by  improved  mechanical  and  chemical  methods.  The  sul- 
phides ortellurides  with  which  the  gold  was  associated  or  combined 
had  to  be  reduced  to  a  state  of  minute  subdivision  by  more  per- 
fect stamping  or  grinding,  and  elaborate  precautions  were  necessary 
to  insure  metallic  contact  between  the  particles  of  gold  and  the 
solvent  mercury.  In  many  cases  the  amalgamation  process  failed 
to  extract  more  than  a  very  moderate  proportion  of  the  gold, 
and  the  quartz  sand  or  'tailings',  which  still  contained  the  re- 
mainder found  its  way  into  creeks  and  rivers,  or  remained  in 
heaps  on  the  ground  around  the  batteries.  In  neighborhoods 
where  fuel  was  available  a  preliminary  roasting  of  the  ore  was 
resorted  to,  to  oxidize  or  volatilize  the  baser  metals  and  set  free 
the  gold  ;  or  the  sulphides,  tellurides,  etc.,  were  concentrated  by 
washing,  and  the  concentrates  were  taken  to  smelting  or  chlor- 
inating works  in  some  favorable  situation  where  the  most  elabor- 
ate metallurgical  methods  could  be  economically  applied.  Many 
efforts  were  also  made  to  apply  the  solvent  action  of  chlorine 
directly  to  the  unconcentrated,  unroasted  ores  ;  but  unfortun- 
ately, chlorine  is  an  excellent  solvent  for  other  substances  besides 
gold,  and  in  practice  it  was  found  that  its  solvent  energy  was 
mainly  exercised  on  the  base  metals  and  metalloids,  and  on  the 
materials  of  which  the  apparatus  itself  was  constructed.  This 
practically  was  the  state  of  matters  in  1889,  when  the  use  of  a 
dilute  solution  of  cyanide  of  potassium  was  first  seriously  proposed 
for  the  extraction  of  gold  from  its  ores,  and  the  proposal  was  far 
from  favorably  regarded  from  a  chemical  point  of  view,  owing 
to  the  various  difficulties  which  presented  themselves.  How 
each  and  all  of  these  difficulties  have  been  swept  aside,  how  within 
little  more  than  a  decade  this  method  of  gold  extraction  has  spread 
over  the  gold-producing  countries  of  the  world,  now  absorbing 
and  now  replacing  the  older  processes,  but  ever  carrying  all  be- 
fore it — all  this  is  already  a  twice-told  tale  which  he  only  felt 
justified  in  alluding  tof  as  they  were  then  meeting  on  the  Rand, 
where  the  infant  process  made  its  debut  nearly  fourteen  years 
ago.  The  Rand  today  is  the  richest  of  the  world's  goldfields, 
not  only  in  its  present  capacity,  but  in  its  potentialities  for  the 
future;  twenty  years  ago  its  wonderful  possibilities  were  unsus- 
pected, even  by  experts.  In  1889  the  world's  consumption  of 


CYANIDE  AS  A  FACTOR  IN  GOLD  PRODUCTION.    11 

cyanide  of  potassium  did  not  exceed  50  tons  per  annum.  At 
present  the  entire  consumption  of  cyanide  is  not  much  short  of 
10,000  tons  per  year,  of  which  the  Transvaal  goldfield  consumes 
about  one-third.  Large  cyanide  works  exist  in  Great  Britain, 
Germany,  France,  and  America,  so  that  a  sure  and  steady  supply 
of  the  reagent  has  been  amply  provided.  In  1894  the  price  of 
cyanide  in  the  Transvaal  was  2s.  per  Ib. ;  today  it  is  8d.  Chem- 
istry has  so  often  been  called  on  to  play  the  part  of  the  humble 
and  unrecognized  handmaiden  to  the  industrial  arts  that  he 
might  perhaps  be  pardoned  if  in  this  case  he  called  public  atten- 
tion to  Cinderella  as  she  shines  in  her  rightful  position  as  the 
genius  of  industrial  initiation  and  direction. 


THE  CYANIDE  PROCESS  AT  GUANAJUATO 
BY  FRANCIS  J.  HOBSON 

(January  6,  1906) 

In  1899  a  number  of  cyanide  tests  were  made  on  Cubo  ore 
by  chemists  in  the  employ  of  the  Mexican  Gold  &  Silver  Recovery 
Co.,  the  owners  of  the  MacArthur  Forrest  patents  in  the  Republic 
of  Mexico.  The  results  of  these  tests  were  far  from  satisfactory. 
The  consumption  of  cyanide  was  low  but  the  extraction  also  was 
low,  averaging  from  40  to  85  %  of  the  silver  and  gold  in 
the  ore.  Most  of  the  tests  were  made  on  samples  weighing  100 
grams,  crushed  to  pass  screens  from  30  to  80-mesh.  In  addition 
to  solutions  of  potassium  cyanide  there  were  added  to  the  charges 
under  treatment,  different  percentages  of  potassium  ferri-cyanide, 
permanganate ,  and  even  ferro-cyanide,  and  to  some  of  them  were 
added  various  amounts  of  sodium  dioxide.  The  time  of  treatment, 
in  nearly  every  case,  was  16  hours.  In  consequence  of  these 
experiments,  the  process  was  condemned  at  Guanajuato.  Shortly 
afterward,  on  the  recommendation  of  E.  A.  Wiltsee  of  the  Venture 
Corporation,  the  Holmes  brothers  experimented  for  several  months 
on  Sirena  and  Cubo  ores  ;  the  results  of  these  further  experiments 
led  them  to  conclude  that  the  ores  of  this  district  could  be  suc- 
cessfully cyanided  by  sliming  everything.  One  point  in  their 
report  was  especially  prominent,  that  even  with  40  days' leaching 
the  sand  resulting  from  crushing  to  40-mesh  gave  no  extraction 
by  treating  with  cyanide  solution.  This  w^as  on  Sirena  ore. 
About  three  and  a  half  years  ago  the  Butters  company  took  up 
the  question  of  cyaniding  the  Sirena  ore,  and  E.  M.  Hamilton, 
of  that  company,  ran  a  series  of  tests  on  a  large  scale  at  the  hacienda 
Pastita,  treating  sand  and  slime  after  ore  concentration  on 
Wilfley  tables;  leaching  the  sand  and  agitating  the  slime.  The 
ore  was  crushed  in  a  stamp-battery  to  pass  a  30-mesh  screen. 
Fifteen  days'  leaching  of  the  sand  with  0.3%  cyanide  solu- 
tion, and  slime  agitation  with  0.05%  solution  gave  excellent  ex- 
traction. The  metals  in  both  cases  were  electrically  precipita- 
ted on  sheet-lead  cathodes.  The  total  extractions  recovered 
by  Mr.  Hamilton  from  two  series  of  tests  showed  92 . 5  and 
94.5%  of  the  total  value  of  the  ore,  the  yield  being  in  concen- 


THE  CYANIDE  PROCESS  AT  GUANAJUATO.         13 

trate  and  bullion.  On  the  basis  of  Mr.  Hamilton's  experiments 
the  Guanajuato  Consolidated  Mining  Co.  installed  the  present 
excellent  plant,  with  a  capacity  of  approximately  200  tons  per  day. 
Two  years  ago  I  was  engaged  by  the  American  Finance  & 
Security  Co.  to  make  a  metallurgical  examination  of  the  Valenciana 
ores.  The  material  treated  first  came  from  the  Guadalupe  dump,  a 
dump  which  contains  about  1,000,000  tons  of  ore.  The  tests 
were  made  on  part  of  the  samples  taken  from  shafts  which  were 
sunk  through  the  dump  in  order  to  ascertain  its  value.  The  tes,ts 
were  made  with  the  5-stamp  mill  and  cyanide  plant  at  the  hacienda 
Central.  First  we  milled  several  lots  of  ore  with  battery  screens 
ranging  from  20  to  30-mesh,  concentrating  on  a  Wilfley  table, 
separating  sand  and  slime  with  spitzkasten  and  spitzlutten.  The 
spitzlutten  were  placed  immediately  under  the  spitzkasten.  An 
excellent  separation  was  obtained,  making  approximately  70% 
of  sand  and  30%  of  slime.  About  500  Ib.  of  sand  and 
150  Ib.  of  the  slime  were  shipped  to  Mexico  City  and  there  sub- 
jected to  experiment  in  the  laboratory  of  the  Mexican  Gold  & 
Silver  Recovery  Co.  Lots  (each  of  5  kilo.)  of  ore  were  leached 
continually,  with  solutions  varying  from  0.1  to  0.7%  KCy  for 
15  days.  In  each  case  the  silver  and  gold  were  precipitated  on  zinc 
shaving.  A  tailing  sample  was  taken  daily  for  15  days,  there 
being  21  sand-charges  under  treatment.  At  the  end  of  12  days 
the  extraction  ceased.  Cyanide  consumption  ranged -from  0.75 
to  1.5  Ib.  per  ton  of  ore  treated.  With  0.3  and  0.4%  solu- 
tions the  extraction  was  equal  to  that  secured  with  stronger  so- 
lutions, and  the  consumption  of  cyanide  was  only  one  pound  per  ton 
of  ore  treated.  The  experiments  on  slime  were  run  on  a  very 
small  scale  at  first,  agitating  in  bottles  with  various  strengths  of 
solution;  a  chemical  extraction  of  about  88%  of  the  silver 
was  obtained  with  0.05%  solution,  with  a  chemical  con- 
sumption of  about  one  pound  of  potassium  cyanide  per  ton  treated. 
Then  tests  were  made  on  a  larger  scale,  using  compressed  air  for 
agitation  and  a  0.05%  solution.  Both  decantation  and 
the  Moore  filter-press  methods  were  tried  for  separating  solution 
from  residue.  Both  were  efficient  but  no  apparent  advantage 
could  be  gained  by  use  of  the  Moore  filter,  the  only  saving  being 
in  cyanide,  and  this  was  so  small  that  there  was  no  profit  in  using 
the  method,  leaving  out  the  question  of  royalties.  The  metals 
were  precipitated  on  zinc  shaving.  Exhaustive  tests  with  zinc- 


14  RECENT  CYANIDE  PRACTICE 

dust  precipitation  were  not  at  all  satisfactory.  To  my  personal 
knowledge  this  was  the  second  case  where  zinc-dust  precipitation 
would  not  work.  With  these  results  for  a  guide,  I  milled  70 
metric  tons  from  the  Guadalupe  dump  at  the  hacienda  Central,  con- 
centrating, separating  sand  from  slime,  and  cyaniding  them 
separately.  I  used  a  0.4%  solution  for  leaching  sand  and 
0.05%  for  agitating  slime.  Approximately  35%  of  the  ore 
value  was  separated  in  the  form  of  concentrate.  We 
obtained  an  extraction  on  sand  of  86%  of  the  silver  and  97% 
of  the  gold;  from  slime  we  extracted  90%  of  the  silver  and  97% 
of  the  gold.  The  time  of  sand-leaching  was  12  days,  and  the 
total  time  of  slime-treatment  was  three  days,  one  day  of  which 
was  active  agitation.  On  sand,  the  consumption  of  cyanide  was 
1.1  lb.,  and  on  slime,  including  mechanical  loss,  it  was  a  trifle 
less  than  2.5  lb.  per  ton  of  dry  slime.  The  metals  were  precipi- 
tated on  zinc  shaving.  A  clean-up  was  made,  the  coarse  zinc 
was  reduced  with  sulphuric  acid,  and  the  product  melted  into 
bullion.  The  two  bars  of  bullion  thus  obtained  contained  in 
gold  2.4c.  per  ton  of  ore  more  than  the  assays  indicated.  The 
silver,  on  the  other  hand,  was  8  gm.,  per  ton  of  ore,  short.  Taking 
into  consideration  the  fact  that  the  precipitation  was  in  a  new 
wood  zinc-box  and  that,  after  the  clean-up  was  made,  it  was  shipped 
to  the  State  of  Michoacan  to  reduce  coarse  zinc  with  acid,  and 
then  melted  four  times  in  order  to  get  bullion  900  fine,  it  could 
not  be  considered  otherwise  than  an  absolute  check  on  the  work. 
A  lot  weighing  100  kg.  of  concentrate  was  shipped  to  Mexico  City, 
one-half  being  leached  without  regrinding;  the  other  half  was  re- 
ground  to  pass  100-mesh,  and  was  then  treated  with  cyanide 
by  the  agitation  and  decantation  method.  In  both  cases  the  met- 
als were  precipitated  on  zinc  shaving1.  The  time  of  treatment 
in  the  first  case  was  90  days  with  0.3%  solution;  in  the  second 
eight  days,  with  the  same  solution.  Total  extraction  was  more 
than  90%.  There  was  no  trouble  in  precipitation.  In  both 
cases  the  clean-up  checked  the  assays  of  heading  and  tailing. 

In  consequence  of  these  experiments,  the  80-stamp  mill  at 
the  Bustos  and  the  cyanide  plant  at  the  hacienda  Flores  are  being 
installed.  I  entertain  no  doubt  of  obtaining  in  practice  results 
equal  to  those  achieved  in  the  laboratory  in  Mexico  City  and  in 
the  experimental  mill  at  the  hacienda  Central.  The  laboratory 
results  and  the  extractions  obtained  in  actual  milling  varied  less 


THE  CYANIDE  PROCESS  AT  GUANAJUATO.         15 

than  one  per  cent.     I  believe  Mr.  Hamilton's  tests  are  being  con- 
firmed in  practice  at  Pastita. 

Two  years  ago  the  owners  of  the  Cubo  mine  installed  a  cyan- 
ide plant  at  their  hacienda.  I  am  not  familiar  with  the  results 
obtained,  but  they  appear  to  be  good  from  the  fact  that  the  plant 
is  still  running.  About  one  year  ago  the  Peregrina  Mining  & 
Milling  Co.  employed  me  to  make  a  metallurgical  examination. 
Results  were  highly  satisfactory,  94%  of  the  precious  metals 
being  extracted  ;  and  the  company  is  operating  a  20-stamp  mill 
and  cyanide  plant;  they  are  now  erecting  an  additional  100 
stamps  with  cyanide  annex.  It  is  stated  that  the  Peregrina  mill 
has  obtained  as  much  as  96%  extraction  of  silver.  George  W. 
Bryant  has  a  cyanide  plant  in  operation  at  the  hacienda  Central, 
and  another  nearly  ready  at  Nayal;  the  extraction  is  satisfactory 
and  this  plant  also  is  being  enlarged.  Frank  G.  Peck,  of  the 
Portland  Mining  Co.  at  Cripple  Creek,  has  purchased,  and  will 
soon  have  erected,  a  40-stamp  mill  and  cyanide  annex  at  the 
hacienda  San  Matias.  Mr.  Ibarguengoitia  has  changed  his  patio 
process  to  cyanidation,  and  is  treating  daily  about  30  tons  of 
custom  ore.  The  Adams  company  at  La  Luz  expects  to 
erect  100  stamps  with  cyanide  plant.  The  Guanajuato  district 
is  now  cyaniding  350  tons  of  ore  daily  ;  with  the  plants  now  pur- 
chased and  under  erection,  this  amount  will  be  increased  shortly 
to  1,400  tons  per  day. 


FINE    GRINDING 

(January  27,   1906) 

The  Editor  : 

Sir — I  have  read  with  interest  the  communication  on  'Fine 
Grinding  in  Metallurgy,'  by  Mr.  E.  E.  Wann,  dated  November  29, 
in  your  issue  of  December  16. 

Mr.  Wann  says,  in  part  :  "Fine  grinding  having  proven  a 
pre-requisite  for  the  highest  extraction  by  amalgamation  and 
cyanide  leaching  of  gold  ores. "By  fine  grinding,  I  take  it  that  Mr. 
Wann  means  crushing  the  material  to  such  an  extent  that  the 
largest  particle  will  be  fine  enough  to  pass  150-mesh  screen.  My 
experience,  gained  in  this  country,  the  Australian  colonies,  and 
Mexico,  leads  me  to  believe  that  in  the  great  majority  of  cases 
such  fine  grinding  is  by  no  means  essential  to  securing  the  best 
commercial  results.  Of  the  number  of  varying  classes  of  ore  I 
have  had  occasion  to  examine  during  my  six  or  seven  years' 
residence  in  the  West,  I  have  met  but  two  or  three  instances  where 
fine  grinding  gave  an  increased  commercial  extraction  of  the  gold 
and  silver  content.  In  most  cases,  where  the  larger  portions  of 
the  crushed  ore  were  fine  enough  to  pass  a  50-mesh  screen,  or, 
in  other  words,  were  approximately  one  one-hundredth  inch  diam- 
eter, a  greater  profit  was  obtained  than  when  the  material  was  pul- 
verized to  slime. 

It  may  be  generally  stated  that,  wherever  careful  classifica- 
tion is  carried  out,  and  absolutely  free  sharp  sand  is  dealt  with 
by  percolation,  results  equally  as  commercially  good  will  be  ob- 
tained from  the  sand  as  from  the  slime,  though,  of  course,  the  treat- 
ment of  the  sand  will  require  probably  four  to  ten  times  as  long 
as  the  slime. 

In  the  somewhat  rare  cases  in  America  in  which  fine  grinding 
will  show  greater  profit  than  average  crushing,  sand  and  slime 
treatment,  I  am  strongly  in  favor  of  the  grinding  pan  as  a  com- 
minutor.  The  pans  in  pairs  are  about  equal  to  one  14-ft.  tube- 
mill  in  capacity,  are  slightly  cheaper  in  operating  and  mainten- 
ance expense,  and  are  about  one-half  the  cost  erected.  If  used  in 
two  series — stage  grinding,  with  intermediate  classification —  it 
is  probable  that  their  capacity  would  be  still  further  increased. 

For  slime  treatment,  either  for  true  slime  or  finely  pulver- 
ized ore,  agitation  in  large,  deep,  flat-bottomed  vats,  fitted  with 


FINE  GRINDING.  17 

revolving  arms,  to  keep  the  solids  from  settling  out  of  the  thin 
pulp  generally  necessary,  and  with  large  centrifugal  pumps, 
drawing  from  the  bottom  and  throwing  to  the  top  for  agitation 
and  aeration  proper,  is  universally  the  most  economical  system. 

Removal  of  the  dissolved  value  can  be  most  economically 
and  perfectly  performed  by  the  use  of  vacuum  filters  of  the  Moore- 
Butters-Cassel  type.  These  filters  are  rapidly  coming  into  use. 
They  are  about  one-half  the  cost,  by  tonnage  treated,  of  the  stand- 
ard-type filter-press,  and  their  operation  is  attended  with  about 
one-third  the  cost.  In  but  very  few  cases  can  an  adequate  ex- 
traction be  obtained  from  the  slime  by  conducting  the  treatment 
in  filter-presses;  it  is  almost  universally  imperative  to  dissolve 
the  metals  by  agitation  prior  to  the  separation  of  the  gold-bear- 
ing liquors  from  the  solids. 

In  the  treatment  of  gold  and  silver  ore,  considerable  time 
is  saved  and  a  slightly  increased  extraction  obtained  if  crushing 
in  the  solvent  be  resorted  to.  For  the  treatment  of  clean  sand  by 
percolation,  more  particularly  silver-bearing  material,  two,  and 
even  in  some  cases  five,  treatments  have  been  found  profitable. 
The  handling  of  this  material  can  be  economically  performed  by 
the  use  of  the  Blaisdell  excavating,  distributing,  and  conveying 
apparatus.  In  a  skillfully  designed  plant,  sand  may  be  moved 
from  one  vat  to  another,  using  the  above  machinery,  for  approx- 
imately one  cent  per  ton,  and  the  extraction  and  profits  enor- 
mously increased. 

As  an  instance  of  the  fallacy  of  attempting  to  fit  the  methods 
of  one  country  to  the  ores  of  another,  may  be  mentioned  the  case 
of  Westren  Australian  ores  and  those  of  Cripple  Creek,  Colorado. 
In  the  former  case,  fine  grinding  is  distinctly  necessary  to  fit  the 
raw  ore  for  the  highest  commercial  extraction,  while  at  Cripple 
Creek  an  almost  equally  good  extraction  may  be  obtained  at  30- 
mesh  as  at  200-mesh,  either  by  bromo-cyanide  treatment  of  raw 
ore,  or  by  simple  cyanidation  of  the  roasted  ore.  As  a  matter  of 
fact,  a  considerably  higher  extraction  may  be  obtained  on  the 
roasted  ore  at  30-mesh  than  upon  the  raw  ore,  using  bromo- 
cyanide  at  200-mesh,  and  finer.  The  ore  in  both  the  above- 
mentioned  districts  has  points  in  common,  that  is,  that  much  of 
the  gold  in  the  material  from  the  lower  levels  of  the  mines  is  com- 
bined with  tellurium. 

GODFREY  DOVETON. 

Denver,  Colo.,  January  8,  1906. 


FILTER-PRESS  PRACTICE    IN   WESTERN 

AUSTRALIA 
BY  A.  B.  WALLACE 

.     (February  3,  1906) 

When  the  mine  operators  in  Western  Australia  turned  their 
attention  to  the  treatment  of  the  gold-bearing  slime,  they  had 
a  choice  of  one  of  two  methods,  namely,  decantation  and  filter- 
pressing.  The  serious  difficulty  was,  and  is,  the  scarcity  and  cost 
of  water.  At  most  mines  at  that  time  the  water  used  for  milling 
was  the  salt  water  which  was  pumped  out  of  the  mines  or  from 
wells.  For  boiler  purposes,  this  water  had  to  be  distilled  and  cost 
from  $1.25  to  $2.50  per  hundred  gallons.  At  the  present  time, 
however,  Kalgoorlie  is  amply  supplied  with  fresh  water  by  the 
'Coolgardie  Water  Scheme,'  as  it  is  called,  which  supplies  about 
5,000,000  gal.  per  day.  This  water  was  pumped  through  a  30-in. 
main  from  the  Swan  river,  a  distance  of  300  miles,  and  is  sold  for 
about  50c.  per  thousand  gallons,  meter  measure.  But  in  other 
districts  beyond  Kalgoorlie,  as,  for  instance,  at  Menzies,  many 
mines  have  to  pay  as  high  as  $5  per  thousand  gallons  of  salt 
water.  For  this  reason,  decantation  methods,  which  involved  the 
loss  of,  on  an  average,  from  300  to  500  gal.,  or  one  or  two  tons  of 
water  per  ton  of  dry  slime  treated,  proved  too  costly,  and,  in  those 
localities,  filter-pressing  was  almost  universally  adopted  as  the 
only  possible  method' of  slime  treatment. 

The  Dehne  press  or  one  of  similar  type  is  almost  universally 
used.  The  presses  are  supplied  with  feed  and  wash  channels' 
through  lugs  attached  to,  but  outside  of,  the  frame.  At  first  it 
was  the  practice  to  collect  the  water  from  the  mill  after  separating 
the  sand  and  allow  the  slime  to  settle,  drawing  off  the  clear  water 
to  be  returned  to  the  mill.  The  slimy  pulp,  in  the  proportion  of 
about  three  of  water  to  one  of  slime  was  then  forced  into  the  press 
by  means  of  compressed  air.  As  soon  as  the  press  was  full  the 
slime  was  treated  for  about  four  hours  by  pumping  cyanide  solution 
through  it.  In  some  cases  compressed  air  also  was  used  to  dry 
the  pulp;  this  method,  however,  took  too  much  press  capacity 
and  was  finally  abandoned. 

The  method  now  used  is  to  collect  the  slime  from  the  mill 


FILTER-PRESS  PRACTICE.  19 

and  agitate  it  in  a  vat  with  mechanical  stirrers,  with  the 
requisite  cyanide  solution,  in  the  proportion  of  two  solution  to  one 
slime,  until  all  the  gold  which  can  be  got  into  solution  is  dissolved 
and  then  filter-pressed,  using  the  filter-press  as  a  separating  mach- 
ine only. 

The  presses  usually  have  had  a  capacity  of  from  three  to  five 
tons  of  dry  slime  per  charge;  the  thickness  of  the  cakes  varies, 
according  to  the  material,  from  one  inch  to  as  much  as  three 
inches.  The  thicker  the  cake,  of  course,  the  more  economical 
the  treatment.  The  size  of  the  cake  is  usually  40  in.  square,  there 
being  from  30  to  50  cakes  in  each  press.  The  filter-cloth  is  material 
specially  woven  for  that  purpose  and  costs  about  50c.  per  yard  at 
wholesale,  so  that  each  cloth  costs  about  $1.25,  and  it  has  a  life 
of  from  30  to  90  days.  If  the  material  pressed  contains  much 
sand,  the  cloth  is  liable  to  get  cut  much  quicker.  One  of  the 
advantages  of  filter-pressing  is  the  large  proportion  of  dissolved 
gold  and  silver  which  can  be  recovered.  When  the  pulp  is  pumped 
or  forced  into  the  press,  practically  70%  of  the  solution  is  recovered 
at  once,  then  a  weak  wash  or  water  is  forced  through  the  cakes. 
The  washing  is  very  thorough,  as  the  water  passes  horizontally 
through  the  slime  from  one  filter-plate  to  the  other,  only  about 
two  tons  of  water  being  necessary  to  wash  one  charge  of  three 
and  one-half  tons  of  slime-.  Compressed  air  is  then  introduced 
under  about  90-lb.  pressure,  which  forces  out  more  of  the  remaining 
water  so  that  the  slime,  when  the  treatment  is  completed,  carries 
only  a  comparatively  small  proportion  of  moisture.  That  percent- 
age of  moisture  varies.  At  the  Lady  Stentonmine,  at  Menzies,  we 
often  had  a  residue  containing  as  little  as  from  11  to  15%  moisture, 
but  I  consider  that  the  average  all  over  the  country  would  be  about 
21  per  cent. 

Regarding  the  cost  of  treatment,  this  varies  so  largely  in 
different  districts  that  it  is  practically  impossible  to  give  an  accurate 
average.  In  Western  Australia  it  may  be  said  to  vary  from  $1.50 
to  nearly  $4  per  ton  of  slime,  depending  on  the  nature  of  the  mate- 
rial on  local  conditions  and  on  the  time  occupied  by  one  complete 
cycle  of  operations.  The  last  is  an  important  factor,  and  it  may 
be  of  interest  to  give  a  few  figures.  First,  with  reference  to  the 
labor  necessary.  It  requires  two  men  to  discharge  a  press  independ- 
ent of  the  'truckers,'  who  convey  the  residue  to  the  dump.  These 
two  men  can  usually  discharge  a  press,  clean  the  frames,  and  close 


20  RECENT  CYANIDE  PRACTICE. 

the  press  ready  for  another  charge  in  from  30  to  45  minutes.  As 
a  rule  two  men  are  employed  for  each  pair  of  presses,  discharging 
and  cleaning  one  while  the  other  is  being  filled  and  dried.  In 
some  mills,  where  it  takes  longer  to  perform  a  cycle  of  operations, 
two  men  can  handle  three  presses.  On  large  plants,  the  shift-boss 
attends  to  the  filling  and  washing,  but  on  smaller  ones  this  is  also 
done  by  the  pressmen,  who  receive  about  $2.80  per  shift  of  eight 
hours.  The  time  occupied  in  filling  a  press  depends  on  the  material 
and  on  the  pressure  used.  As  a  rule,  the  pulp  is  forced  under 
a  pressure  of  from  60  to  100  Ib.  per  sq.  in.  and  the  press  is  filled 
in  from  20  to  30  minutes.  Wash  water  is  then  used 
for  from  15  to  25  minutes,  and  generally  compressed  air  to  dry 
the  slime  is  admitted  for  about  10  minutes;  the  full  cycle  of  opera- 
tions, including  the  discharging  and  cleaning,  being  completed 
in  about  two  hours.  Thus,  at  Menzies,  two  men,  using  two  presses, 
handle  seven  charges  in  an  eight-hour  shift,  or  about  27  short 
tons  of  dry  slime. 

The  heavy  labor  cost  is  due  chiefly  to  the  difficulty  of  getting 
rid  of  the  residues;  these  are  taken  away  in  cars  and  frequently 
have  to  be  hauled  some  distance  over  the  flat  site  on  which  the  mill 
is  necessarily  erected  in  a  flat  desert  country.  Power  is  also  an 
expensive  item  when  fuel  costs  from  $6  to  $7.50  per  cord,  and  water 
for  boilers  has  to  be  distilled  or  bought.  On  the  other  hand,  the 
method  could  be  used  economically  in  a  district  where  there  was  a 
plentiful  supply  of  water,  as  the  residues  could  be  sluiced  away 
and  water  could  be  used  to  supply  power  both  for  agitation  and 
for  compressing  air. 

Of  late  it  has  been  the  custom  to  use  pumps  for  filling  the 
presses  instead  of  compressed  air,  as  being  cheaper,  but  when  this 
is  done,  a  large  air-chamber  must  be  added  to  produce  as  steady 
a  pressure  as  possible. 

The  Diehl  process,  which  involves  the  sliming  of  all  the  ore, 
has  been  employed  with  great  success  at  some  of  the  large  proper- 
ties. This  described  briefly  is  as  follows:  The  ore,  after  crush- 
ing and  amalgamating,  is  sized,  the  fine  slime  going  direct  to  the 
agitation  vats,  and  the  coarse  sand  going  to  flint  or  tube-mills  for 
re-grinding.  The  product  from  these  is  again  sized  and  the  coarse 
material  returned,  the  fine  going,  as  before,  to  the  agitation  vats, 
which  only  receive  the  ore  after  it  is  ground  to  slime.  It  is  then 
agitated  with  cyanide  solution  for  a  period  varying  from  16  to 


FILTER-PRESS   PRACTICE.  21 

24  hours,  then  a  solution  of  bromo-cyanide  is  added  and  the  agita- 
tion continued  for  a  further  period,  after  which  the  whole  is  filter- 
pressed.  This  method,  on  the  whole,  has  been  highly  successful 
in  Western  Australia  and  owing  to  the  peculiar  local  conditions, 
was  the  only  one  possible.  In  many  cases,  slime  has  been  treated 
which  had  accumulated  in  the  settling  dams.  This  is  taken  in 
cars  to  a  'mixer,'  in  which  the  slime  is  thoroughly  broken  up  in 
cyanide  solution,  after  which  the  treatment,  of  course,  is  the 
same  as  previously  described. 


CYANIDATION  OF  CONCENTRATE 

BY  FRANCIS  J.  HOBSON 

(February  3,  1906) 

It  is  generally  held  that  gold  as  it  exists  in  concentrates,. 
is  soluble  in  potassium  cyanide,  and  the  adaptability  of  the  cyanide 
process  depends  entirely  upon  the  physical  characteristics  of  the 
concentrate  to  be  treated,  the  relative  association  of  the  crystal- 
line particles;  provided,  there  are  no  base  metals  present  to  cause 
an  excessive  consumption  of  cyanide  and  consequent  fouling  of 
solutions. 

In  the  case  of  silver,  the  question  arises  as  to  the  solubility 
of  the  various  natural  occurrences  of  the  metal  as  well  as  the 
physical  and  chemical  characteristics  of  the  concentrate. 

The  chief  minerals  of  silver  are:  The  native  metal  and  the 
sulphide,  argentite;  four  species  among  the  sulph-arsenites  and 
sulph-antimonites,  namely,  proustite,  or  ruby  silver;  pyrargyrite, 
dark  red  silver;  freieslebenite,  antimonial  silver-lead  sulphide;, 
stephanite  or  brittle  silver;  the  bromide  and  chlorobromide, 
bromyrite  and  embolite.  Argentiferous  tetrahedrite  contains 
sometimes  as  high  as  30%  silver  as  argentite;  there  is  also> 
argentiferous  galenite  and  blende  containing  silver  as  sulphide. 

The  first  mentioned,  native  silver,  is  so  slowly  soluble  in  cyan- 
ide that  from  it  practically  no  extraction  can  be  obtained.  Argen- 
tite is  readily  soluble,  likewise  the  chloride,  bromide,  and  chloro- 
bromide. Ruby  silver,  stephanite,  and  freieslebenite,  are  spar- 
ingly soluble  in  cyanide  solutions  but  they  are  readily  soluble 
in  a  solution  of  mercurous  potassic  cyanide.  The  extraction  of 
silver  by  cyanide  from  argentiferous  galenite,  is  a  problem  yet 
to  be  solved. 

Taking  these  facts  as  a  basis,  in  the  absence  of  chemical  inter- 
ference, silver  can  be  extracted  from  concentrates  where  it  exists 
in  soluble  form,  if  the  physical  structure  permits  of  solution-con- 
tact with  the  contained  argentiferous  compound.  I  have- 
proved  in  the  case  of  concentrates  from  Veta  Madre  ore,  that 
the  physical  structure  will  permit  contact  sufficient  for  the  extrac- 
tion of  both  silver  and  gold  without  the  fouling  of  solutions.  I 
leached  100  Ib.  of  concentrate  obtained  from  ore  crushed  by 


CYANIDATION  OF  CONCENTRATE.  23 

stamps  to  pass  a  30-mesh  screen.  This  material  was  treated 
continuously  for  90  days  with  0.3%  KCy  solution.  An 
extraction  of  89%  of  the  silver  and  97%  of  the  gold 
was  obtained,  an  extraction  of  91.5%  of  the  total  value. 
The  metals  were  precipitated  on  zinc  shaving  in  a  porcelain  zinc- 
box;  the  clean-up  checked  with  the  extractions  called  for  by  assay; 
all  of  the  zinc  was  reduced  with  acid. 

One  hundred  pounds  of  concentrate,  re-ground  to  pass  a  100- 
mesh  screen,  \vere  treated  by  agitation  in  a  revolving  barrel  with 
a  0.3  %  cyanide  solution,  for  eight  days,  decanting  and  renew- 
ing solution  daily.  The  extraction  obtained  was  93.5%  of 
the  silver  and  96  of  the  gold.  I  believe  that  30  days'  leaching  of 
the  Te-ground  concentrate  would  have  given  an  equally  good 
result.  The  cyanide  consumption  in  both  tests  was  seven  kilo- 
grams per  ton.  The  concentrate  was  low-grade,  assaying  about 
four  kilograms  silver  and  30  grams  gold  per  metric  ton. 

I  am  now  running  a  test  in  my  laboratory  on  a  100- kilo. 
charge  of  concentrate,  assaying  26.5  kilo,  silver  and  130  grams 
gold.  Silver  exists  in  the  concentrate  chiefly  as  argentite.  It  is 
being  leached  with  0.7%  solution.  So  far  it  does  not  show 
an  excessive  consumption  of  cyanide,  and  after  seven  days'  leach- 
ing the  extraction  of  silver  was  about  20%.  After  leaching 
for  six  weeks,  the  extraction  is  53%  of  the  silver  and  80% 
of  the  gold.  Leaching  is  still  going  on.  Comparing  this 
result  with  that  obtained  in  the  same  time  in  the  90  days'  leach, 
I  expect  a  like  extraction  with  three  months'  leaching.  At  first 
this  may  seem  to  be  an  exceedingly  long  time  of  treatment,  but 
when  you  consider  that  from  ores  in  this  camp,  less  than  one  per 
cent  of  concentrate  by  weight  of  ore  is  obtained,  a  small  addition 
to  our  cyanide  mills  will  take  care  of  our  concentrate  output.  In 
the  case  of  the  Guanajuato  Mines  &  Reduction  Company's  plant, 
we  are  erecting  sand-vats  each  of  350-tons  capacity.  Two  addi- 
tional vats  will  handle  concentrate,  although  it  will  doubtless  be 
better  to  put  in  three  vats  one  half  the  size  of  our  sand-vats.  This 
will  allow  for  six  weeks'  collecting  of  concentrate  and  three  months' 
leaching.  The  sand-mill  solution  can  be  used  for  this  purpose 
without  interference  with  sand  treatment.  The  precipitation 
can  take  place  in  the  sand-solution  zinc-boxes. 

I  am  of  the  opinion  that  concentrate  from  other  ores  of  the 
Guanajuato  district  will  be  less  amenable  to  cyanide  treatment  than 


24  RECENT  CYANIDE  PRACTICE. 

those  from  the  Veta  Madre,  as  considerable  value  is  carried  in 
arsenopyrite  whose  molecular  structure  is  more  compact  than  that 
of  the  pyrite;  consequently,  if  the  extraction  can  be  obtained, 
it  will  be  by  longer  contact,  as  a  more  compact  structure  will 
necessarily  cause  slower  diffusion  of  solution. 

The  best  method  of  treating  our  concentrates  is  likely  to  be 
by  leaching  with  cyanide  solution  for  periods  of  from  30  to  180 
days,  followed  by  chloridizing  roasts  and  further  leaching  with 
cyanide.  The  objection  will  be  made  that  returns  of  bullion 
from  the  concentrate-leaching  will  be  greatly  delayed,  but  it  will 
not  be  as  long  as  the  length  of  treatment  suggests,  because  the 
larger  part  of  the  extraction  will  be  obtained  in  the  earlier  period 
of  leaching,  and  this  bullion  will  be  recovered  as  it  is  extracted,. 
in  the  regular  clean-up. 


The  Editor  : 


FINE  GRINDING 

(February  3,  1906) 


Sir — In  the  discussion  on  this  subject  in  your  issues  of  Decem- 
ber 16  and  January  27,  several  interesting  questions  arise.  Is 
fine  grinding  necessary  to  the  highest  extraction  by  cyanide? 
Does  fine  grinding  improve  amalgamation  ?  Are  the  best 
commercial  results  obtained  by  fine  grinding  ?  Mr.  Doveton's 
definition  of  the  term  will  bear  amplifying.  In  this  country 
'fine  grinding'  is  generally  understood  to  mean  a  secondary  com- 
minution of  the  mill-tailing  through  150-mesh  or  finer,  after  the 
usual  mill  treatment  by  amalgamation  and  concentration,  or  both. 
All  the  parties  to  this  discussion  seem  to  be  of  one  opinion  as  to 
the  effectiveness  of  this  secondary  grinding.  Even  Mr.  Doveton, 
who  is  apparently  not  a  very  warm  advocate  of  the  system,  con- 
cedes, by  implication,  that  it  aids  extraction,  but  is  only  in  a 
few  instances  commercially  profitable.  It  seems  to  be  a  settled 
fact  then  that  cyanide  solutions  will  yield  the  highest  extraction 
from  finely  crushed  material.  The  exceptions  to  this  are  so  rare 
that  the  fact  may  be  safely  accepted  as  one  of  the  axioms  of 
cyaniding. 

The  effect  of  fine  grinding  on  amalgamation  is  a  subject 
which,  curiously  enough,  has  been  thrust  into  prominence  by 
recent  developments  in  cyaniding.  I  do  not  know  of  any  instance 
where  amalgamation  is  used  after  the  fine  grinding  or  sliming  oper- 
ation; although  it  is  said  to  have  been  tried  with  some  success- 
in  South  Africa  and  in  Korea.  I  think  it  has  been  the  exper- 
ience of  mill-men  that  crushing  finer  than  the  approved  and  trad- 
itional 30  or  40-mesh  rather  hinders  than  aids  amalgamation. 
In  the  Goldfield  district,  Nevada,  the  practice  is  to  re-crush  the 
coarsest  of  the  16  or  20-mesh  product  from  the  stamps  in  Hunt- 
ington  and  Bryan  mills.  This  has  the  effect  of  brightening  the 
characteristically  reddish-colored  gold  of  the  district,  as  well  as 
to  release  the  mineral  imbedded  in  the  coarse  particles  of  quartz, 
and  the  use  of  large  amalgamating  plates  after  the  second  crush- 
ing has  been  of  distinct  advantage.  My  belief  is  that  amalgam- 
ation, in  cases  where  the  gold  does  not  amalgamate  readily  and 


26  RECENT  CYANIDE  PRACTICE. 

where  re-crushing  is  necessary  for  the  highest  extraction  by  cyan- 
ide, may  be  best  carried  on  in  two  stages,  especially  where — as 
in  the  case  of  the  Combination  mill  at  Gpldfield — the  second  crush- 
ing does  not  reduce  the  ore  to  finer  than  40-mesh.  When  Mr. 
Wann  speaks  of  "fine  grinding  having  proven  a  pre-requisite  for 
the  highest  extraction  by  amalgamation  and  cyanide  leaching  of 
gold  ores,"  he  implies  that  it  is  now  considered  an  essential  to  good 
amalgamation.  It  would  be  interesting  to  know  of  the  special 
instances  wherein  this  practice  has  improved  amalgamation. 

Mr.  Doveton's  views  on  fine  grinding,  discrediting  this  aid  to 
high  extraction  as  commercially  unprofitable,  will  be  received 
with  some  surprise  by  companies  now  using  tube-mills  in  this 
country  and  in  Mexico.  Several  such  mills  are  in  operation  at 
El  Oro ;  Mr.  Butters  is  installing  them  on  his  Mexican  properties ; 
the  Liberty  Bell  company  at  Telluride,  Colorado,  and  the  Stand- 
ard company  at  Bodie,  California,  have  tube-mills  in  operation, 
apparently  at  a  cost  per  ton  which  justifies  their  use.  If  fine 
grinding  is  a  commercial  success  in  Australia  and  at  the  various 
properties  above  named,  all  working  on  dissimilar  ores,  it  must 
have  decided  merits.  Obviously,  the  profitableness  of  this  addi- 
tional grinding  will  depend  in  each  case  on  the  margin  of  saving. 
If  sliming  a  $2  sand  will  raise  the  extraction  by  cyanide  from 
80  to  90%  and  the  operation  costs  50c.  per  ton,  manifestly  it 
will  not  pay.  But  if  such  an  increase  of  saving  is  made  on  $10 
sand,  it  will  pay.  It  seems  impossible  to  generalize  briefly  in 
estimating  the  value  of  a  process,  the  success  of  which  must  de- 
pend upon  so  many  inherent  conditions.  My  own  experience 
in  fine  grinding  has  been  somewhat  happier  than  Mr.  Doveton's  ; 
though  I  must  admit  that,  while  an  advocate  of  this  method,  I 
have  not  had  occasion  until  recently  to  install  a  tube-mill  or  grind- 
ing-pan.  What  knowledge  I  have  of  the  subject  has  been  gathered 
from  experimental  work  and  from  available  data  of  plants  in 
operation.  I  assume  that  Mr.  Doveton  has  drawn  his  conclusions 
from  reliable  results,  that  is,  from  fair  tests  on  a  working  scale 
over  a  considerable  period.  Obviously  a  mere  experimental  test 
to  determine  cost  of  treatment  would  not  be  conclusive.  Those 
interested  in  this  important  subject  would  be  glad  to  know  spec- 
ifically from  Mr.  Doveton  the  cases  in  which  he  met  with  failure 
in  plants  resorting  to  fine  grinding  on  a  scale  large  enough  to  afford 


FINE  GRINDING.  27 

reliable  data.     Such  information  would  be  of  special  value  at  the 
present  time. 

.  In  the  treatment  of  silver  ores  by  cyanide  I  am  disposed 
to  take  a  middle  ground  between  the  extreme  views  held  by  Mr. 
Wann  and  Mr.  Doveton.  Agitation  of  finely  crushed  silver  ores 
for  the  long  period  usually  required  for  the  best  extraction  is  in 
most  cases  neither  practicable  nor  economical.  In  the  treatment 
of  such  ores  I  have  obtained  the  best  commercial  results  by  re- 
grinding  to  a  fine  sand  (60  or  80-mesh)  and  leaching  this  product 
from  15  to  20  days,  after  a  careful  separation  of  the  slime.  The 
pure  slime,  by  reason  of  the  fine  state  of  division  of  the  mineral, 
does  not  require  more  than  three  or  four  days'  agitation  for  the 
best  results. 

Mr.  Doveton  calls  timely  attention  to  the  Blaisdell  apparatus 
for  emptying  and  filling  tanks,  and  for  carrying  sand  from  one 
tank  to  another.  The  merits  of  this  system  from  all  points  of 
view  were  tried  and  proved  at  the  Butters  plant  at  Virginia  City. 
I  am  informed  that  two  large  cyanide  plants  now  in  course  of 
erection  in  Mexico  are  to  be  equipped  with  this  apparatus,  as 
well  as  the  new  500-ton  cyanide  plant  of  the  Tonopah  Mining  Co., 
at  Tonopah,  Nevada.  In  districts  where  the  price  of  labor  is 
high,  or  where  cheap  labor  is  uncertain  and  unreliable,  as  in  parts 
of  Mexico,  the  value  of  mechanism  of  this  sort  is  incalculable. 

The  evolution  of  slime  filtering  is  one  of  the  most  interesting 
of  recent  developments.  Filter-presses  were  never  popular  or 
much  used  in  America.  The  Moore  process,  at  first  installed  at 
the  Golden  Gate  mill  at  Mercur,  Utah,  was  soon  discarded,  but 
was  later  introduced  at  the  Lundberg  &  Dorr  mill  at  Terry,  South 
Dakota,  at  the  Liberty  Bell  mill  in  Colorado,  and  at  the  Standard 
Co.'s  mill,  at  Bodie,  California.  At  all  of  these  places  it  is  said 
to  be  operating  successfully.  Cassel  introduced  an  important 
modification  of  the  Moore  filter  by  practically  reversing  the 
operation,  that  is,  conveying  the  pulp  and  the  various  solutions 
to  a  box  carrying  stationary  filters,  instead  of  shifting  the  filters, 
as  in  the  Moore  scheme.  The  merits  of  these  two  types  of  filters 
were  thoroughly  investigated  at  Virginia  City,  where,  after  sev- 
eral months  of  quiet  and  earnest  work,  the  Butters-Cassel  filter, 
so  called,  was  finally  evolved.  This  is  now  in  use  at  the  Butters 
plant,  where  150  tons  of  slime  per  day  are  being  filtered  at  a 
cost  of  life,  per  ton.  The  system  is  very  simple  and  works 


28  RECENT  CYANIDE  PRACTICE. 

with  a  convincing  smoothness  and  precision  which  appeal  at  once 
to  the  practical  eye.  At  the  mill  of  the  Combination  Mines  Co. 
at  Goldfield,  this  process  is  being  installed  to  treat  40  tons  of 
high-grade  slime  per  day.  The  filter-press  which  has  been  in 
service  for  several  months  will  be  discarded  as  too  expensive  to 
operate. 

FRANCIS  L.  BOSQUI. 
San  Francisco,  January  27,  1906. 


FINE  GRINDING 

(Editorial,  February  10,  1906) 

The  contributions  of  Messrs.  Bosqui  and  Doveton  on  this 
interesting  subject  ought  to  elicit  further  useful  discussion.  A 
few  definitions,  or  at  least,  an  agreement  as  to  the  precise  meaning 
of  the  terms  employed,  may  prevent  confusion.  Mr.  Henry  Louis, 
professor  of  mining  at  the  Durham  College  of  Science,  has  sug- 
gested that  we  use  specific  terms  to  describe  the  various  stages 
of  grinding;  'breaking'  to  be  confined  to  coarse  breaking  of  crude 
ore;  'crushing'  for  smaller  division  by  pressure  or  impact;  'grind- 
ing' for  comminution  by  attrition.  The  idea  of  technical  terms  is 
not  to  invent  new  or  high-sounding  words,  but  to  secure  precision 
by  giving  individual  words  a  particular  duty.  'Re-grinding'  and 
'sliming'  are  often  used  interchangeably,  but  they  do  not  refer 
to  an  identical  process;  re-grinding  is  an  intermediate  operation 
which  often  precedes  the  final  reduction  to  slime.  Two  separate 
products  are  made  sometimes,  as  in  the  cyanidation  of  silver 
ores,  in  the  two  operations  referred  to;  in  other  cases  only  one  prod- 
uct is  obtained  by  a  two-stage  process.  As  to  'sand'  and 
'slime',  we  have  had  a  good  deal  of  clever  dissection  of  these 
tefms;  the  last  word  of  precision  was  said  when  slime  was  de- 
fined, by  Mr.  A.  W.  Warwick,  as  a  colloid  hydrate;  but  this  is  the 
chemist's  not  the  millman's  point  of  view.  To  the  millman, 
'sand'  and  slime'  express  a  condition  and  not  a  theory.  Formerly 
a  product  of  extreme  pulverization,  so  finely  comminuted  as  to 
be  unleachable,  was  called  'slime'.  But  we  have  changed  all  that; 
filtering  has  been  so  developed  that  solutions  can  be  forced 
through  material  once  regarded  as  impermeable,  and  slime  is 
willfully  made  because  the  extreme  subdivision  of  particles 
which  it  represents  is  favorable  to  quick  solution  in  the  presence 
of  certain  chemicals,  such  as  potassium  cyanide. 

Slime  is  no  longer  an  unleachable  product.  We  have  returned 
to  the  old  definition  which  depended  on  sizing,  and  for  the  mo- 
ment the  arbitrary  limit  is  150-mesh,  simply  because  that  degree 
of  comminution  is  found  by  practice  to  give  the  best  results  in 
the  presence  of  two  economic  factors,  the  cost  of  reducing  the  size 
of  the  particles  and  the  time  required  for  solution  of  the  precious 


30  RECENT  CYANIDE  PRACTICE. 

metals.  Unless  made  sufficiently  small,  the  cyanide  cannot  get 
at  the  gold  encased  in  the  quartz.  Meanwhile  'sand'  continues, 
to  be  the  granular  product,  with  sharp  edges,  readily  percolable 
by  solutions.  The  tendency  is  to  decrease  the  proportion  of 
this  product  by  re-grinding  it  to  the  consistence  of  slime.  Such 
'sand'  when  re-ground  to  150-mesh  is  not  'slime'  in  the  eyes  of 
a  microscopist,  because  the  particles  are  sharp,  they  are  not 
colloid;  but  the  cyanide  expert  who  knows  all  these  things,  will 
call  this  product  'slime'  just  as  much  as  the  clay  or  mud  produced 
in  the  first  instance  from  the  soft  aluminous  or  feldspathic  con- 
stituents of  the  ore.  It  is  'slime'  to  him  because  he  gives  it  the 
treatment  alloted  to  slime.  In  other  words,  'sand  and  'slime" 
are  two  mill  products  ;  they  are  not  based  on  nice  chemical  or 
physical  distinctions  and  they  serve  their  present  purpose. 
Anything  finer  than  150-mesh  is  slime,  anything  coarser  than 
100-mesh  is  sand,  anything  between  is  an  accidental  by-product. 
Being  based  on  no  true  scientific  distinction,  we  expect  to  see 
-these  terms  discarded  as  cyanide  practice  becomes  further  devel- 
oped. 


FINE  GRINDING 

(Feburary  17,    1906) 

The  Editor  : 

Sir — As  one  whose  experience  in  ore-grinding  began  36  years 
ago  and  who  subsequently  has  been  almost  uninterruptedly  assoc- 
iated with  it,  I  am  pleased  that  interest  seems  to  be  taken  in 
the  public  discussion  of  the  subject.  It  is  be  hoped  that  a  gen- 
erous spirit  will  prevail  and  no  bitterness  engendered. 

With  some  ores,  values  are  pretty  well  released  without  very 
fine  comminution,  while  I  believe  that  we  of  the  United  States 
have  generally  erred  in  not  making  our  pulp  fine  enough.  Our 
patio  neighbors  to  the  south  of  us  have  always  in  the  past  excelled 
our  work  in  that  respect.  They  have  been  content  with  their 
slow-going  arrastres  and  unmodernized  Chilean  mills,  in  which  the 
coarser  particles  settle  to  the  effective-crushing  zone  while  the 
finer  particles  float  above. 

We  early  evolved  the  pan,  with  a  faster  motion,  to  grind 
as  well  as  to  amalgamate,  but  in  this  there  is  no  systematic  selection 
of  the  particles  most  needed  to  pass  the  grinding  surfaces.  The 
pan  served  the  purpose  when  we  knew  no  better,  and  strange  to 
say  it  still,  by  some,  seems  to  be  considered  an  economical  grinder. 
More  than  20  years  ago  I  departed  from  this  practice  by  intro- 
ducing special  grinding  pans  in  which  the  pulp  passed  once  under 
a  muller  having  a  solid  ring  disc  and  thence  out  of  the  pan  to 
another  of  the  same  kind,  if  finer  pulp  was  desired.  These  were 
decidedly  better  and  more  economical  than  the  amalgamating 
pan,  used  as  a  grinder;  yet  they  were  not  as  efficient  and  desir- 
able as  a  grinder  adopted  some  16  years  ago  which  was  of  the 
old  buhr-stone  flour-mill  type,  made  entirely  of  metal,  and  run 
at  a  high  speed.  Where  the  bottom  disc  revolves  instead  of  the 
upper,  the  sand  particles  rotate  better  between  the  two  discs  at 
the  period  of  crushing,  and  so  cut  the  metal  to  a  less  extent, 
and  also  the  crushed  particles  pass  more  quickly  away.  Un- 
doubtedly no  method  of  grinding  between  two  parallel  surfaces 
of  metal  can  surpass  this  simple  and  almost  primitive  device, 
and  the  cost  of  it  is  probably  less  than  that  of  any  other  machine 
of  like  capacity.  Yet  all  grinding  between  parallel  surfaces  un- 
avoidablv  involves  considerable  loss  of  shoe  and  die  metal. 


32  RECENT  CYANIDE  PRACTICE. 

Power  is  consumed  by  that  as  well  as  by  any  other  means 
of  making  a  hard  ore  very  fine.  When  one  considers  the  square 
surface  area  of  cleavage  involved  in  breaking  a  ton  of  ore  to  pass 
a  200-mesh  screen,  the  power  involved,  without  allowing  for  loss 
in  its  mechanical  attainment,  appears  formidable  in  ratio  with 
the  hardness  and  toughness  of  the  ore  in  hand.  If  a  solid 
cube  of  rock  weighing  one  ton  is  cut  into  cubes  measuring  V-ioo 
of  one  inch,  it  involves  a  cleavage  af  approximately  15,600  square 
feet  ;  yet  if  a  sample  could  be  had  solely  of  such  small  cubes, 
it  would  appear  as  fine  sand  and  not  as  slime.  It  is  quite  probable 
that  a  pulp  that  has  passed  a  200smesh  screen  would  more  nearly 
represent  three  or  four  times  the  aforementioned  area  of  cleavage. 

It  is  not  possible,  at  least  commercially,  to  obtain  as  fine  a 
product  from  grinding  between  two  parallel  surfaces  of  metal 
as  that  produced  by  a  tube-mill,  still  it  is  not  yet  safe  to  say 
that  there  are  no  situations  wherein  the  grinder  is  more  advan- 
tageous*than  the  tube-mill,  and  this  without  reflection  upon  the 
success  of  the  latter. 

The  commercial  profit  line  is  affected  by  characteristics  of 
environment  as  well  as  characteristics  of  an  ore,  and  in  one 
locality  it  might  be  profitable  to  grind  an  ore  finer  than  the  same 
ore  in  another  locality,  so  that  every  individual  case  must  be 
determined  apart.  Data  of  costs  and  conditions  bearing  upon 
other  ores  when  treated  by  different  means,  are  an  assistance  in 
forming  a  decision  as  to  what  course  to  pursue  in  any  given  case  ; 
but  decision  must  be  made  by  individual  judgment  and  not  by 
fixed  rule. 

M.   P.   Boss. 

San  Francisco,  February  12,  1906. 


MILLING  V.   SMELTING    IN     THE    TREATMENT 
OF  TONOPAH-GOLDFIELD  ORES 

BY   FRANCIS  L.   BOSQUI 

(March  31,  1906) 

The  report  that  Mr.  Charles  Schwab  has  entered  into  a  smel- 
ter contract  for  the  treatment  of  his  Nevada  ore  raises  the  ques- 
tion as  to  how  far  smelters  can  compete  with  local  mills 
in  the  treatment  of  the  silicious  ores  of  the  southern  Nevada 
district.  I  have  been  for  some  time  of  the  opinion  that  this  in- 
teresting field  does  not  offer  an  encouraging  prospect  to  the 
smelter.  Recent  experiments  have  shown  conclusively  that  the 
representative  ore  of  the  Tonopah-Goldfield  district — not  including, 
of  course,  the  higher  grade  silver-lead  ores  of  the  outlying 
country — can  be  handled  by  modern  mill-processes  to  far  better 
advantage  than  by  smelting,  at  the  current  freight  and  smelter 
rates.  At  Goldfield,  at  the  present  time,  it  is  unlikely  that  the 
smelter,  even  with  much  reduced  rates,  can  hope  to  compete 
with  the  phenomenally  high  extraction  obtained  from  oxidized  ore 
at  the  Combination  Mines  Co.'s  mill,  the  only  milling  plant  in 
the  district  in  continuous  operation.  From  other  properties  at  Gold- 
field  shipments  are  being  made  to  the  smelters,  but  only  because 
of  the  lack  of  efficient  reduction  plants.  A  large  and  picturesque 
variety  of  small  custom  mills  have  been  in  desultory  operation 
at  Goldfield  for  a  year  or  more;  but  these  have  -been  hampered 
by  scarcity  of  water,  in  some  instances  by  lack  of  capital  for  pro- 
per equipment,  and  possibly,  by  unskilled  management.  The 
lively  competition  between  these  mills  has  resulted  in  the  adop- 
tion of  ridiculously  low  rates  for  custom-milling,  and  prepos- 
terous guarantees  of  extraction,  involving  a  hard  and  unprofitable 
struggle.  This  has  had  the  logical  effect  of  discrediting  milling 
in  general,  and  has  reacted  somewhat  in  favor  of  the  smelters. 
And  until  other  mines  follow  the  lead  of  the  Combination  company 
and  erect  their  own  plants,  this  will  probably  continue  to  be  the 
status  of  milling  in  the  Goldfield  district.  It  is  true  that  the  present 
scarcity  of  water  in  the  immediate  vicinity  is  a  serious  obstacle 
to  milling  on  a  large  scale ;  but  this  is  not  by  any  means  insur- 


34 


RECENT  CYANIDE  PRACTICE. 


mountable  if  mine  owners  will  only  be  convinced  of  the  advantage 
of  owning  and  operating  their  own  plants. 

At  the  Combination  mill  the  expediency  of  treating  ore  under 
$50  per  ton,  where  an  extraction  of  90%  and  better  is  obtained, 
is  so  obvious  that  no  attempt  has  been  made  to  ship  material 
of  this  grade.  In  fact  it  has  not  been  customary  to  send  any- 
thing to  the  smelter  under  20  oz.  gold  per  ton. 

The  following  interesting  calculation  of  comparative  net  prof- 
its from  shipping  and  milling  high-grade  ore  from  the  Combin- 
ation mine  was  made  to  determine  to  what  point  milling  could 
be  profitably  carried.  This  table  is  based  upon  the  Selby  Smel- 
ting &  Lead  Co.'s  schedule  for  September,  1905,  as  follows: 


<J 

IT) 

2 

~ 

S3 

~ 

e 

"2.  p  3 

CD 

o"S  5's 

of 

81 

£^  "-j 

2. 

^|E<S 

S 

1 

j? 

(Tg; 

3 

S-  ^'8 

3 

3? 

re 

*d  " 

i/i 

P    ^  "       c^ 

Gfl 

5' 

1 

8| 

CO     P 

3* 

5*2.2  p 

3 

0>    r+ 

3 

3  ^§  ^ 

3 

0 

o 

O  "U, 

(75 

^  rf  ^* 

3 

ft) 

3 

!    QfQ   3'  "—  ' 

3; 

o 

• 

2- 

'.     p  ^  w 

3s 

ft 

ro 

•       fl*  OS  CO 

3' 

Crq 

• 

' 

$200 

$48.20 

$151.80 

$26 

$174 

Milling,     $22  .  20  per  ton 

300 

50.30 

249.70 

36 

264 

14.30 

400 

57.90 

342.10 

46 

354 

11.90 

500 

65.50 

434  .  50 

56 

444 

9.50 

600 

65.60 

534  .  40 

66 

534 

Shipping,      0  .  40 

700 

71.95 

628.05 

76 

624 

4.05 

800 

78.30 

721.70 

86 

714 

7.20 

Freight  rate  from  Goldfield  to  smelter,  $22  per  ton  for  ores  assaying 
above  10  oz.  gold  per  ton;  with  an  increase  of  3%  for  valuation  above 
$300  per  ton. 

Smelter  discount,  $1.17  per  oz.  of  gold  for  ore  assaying  under  15  oz.; 
smelter  discount,  $0.92  per  oz.  of  gold  for  ore  assaying  between  15  and  30 
oz.;  smelter  discount,  $0 . 67  per  oz.  of  gold  for  ore  assaying  30  oz.  and  above; 
$1  per  ton  haulage  from  mine  to  railroad  depot;  $3  per  ton  cost  of  sacks 
and  sacking. 


It  will  be  seen  from  the  above  that  at  the  Combination  mine 
it  is  more  profitable  to  mill  than  to  ship  ore  running  even  as  high 
as  $600  per  ton,  assuming  an  extraction  of  90%.  And,  in  prac- 
tice, ore  of  this  grade  is  being  used  to  'sweeten'  the  lower  grade 
material  to  make  a  milling  product  of  about  5  oz.  gold. 


MILLING  v.  SMELTING.  35 

It  should  be  explained  in  this  connection,  and  with  reference 
to  the  above  table,  that  milling  costs  and  losses  would  be  still 
further  increased  by  the  amount  of  discount,  freight,  and  treat- 
ment of  concentrate,  cyanide  products,  and  bullion,  reducing  cor- 
respondingly the  net  returns  and  profit  by  miHing.  On  the  other 
hand,  an  increase  of  two  or  three  per  cent  in  mill-saving  over 
90%  would  very  considerably  raise  the  net  returns  from  milling. 

The  following  record  of  a  working  test  made  at  the  Com- 
bination mill,  on  comparatively  high-grade  ore,  has  a  bearing 
on  this  point: 

Tons- treated,  according  to  actual  weight,  63.212;  tons 
treated,  by  estimate  of  various  products,  63.18,  determined  as 
follows  :  Slime,  14.4  tons  ;  concentrate,  0.78  ton  ;  sand,  48  tons. 

Bullion  recovery:  813.1  oz.  amalgam,  or  244.3  oz.  bullion 
0.942  fine,  or  230  oz.  fine  gold. 

Concentrate  recovery:  0.779  ton,  assaying  24.57  oz.  gold, 
or  19. 14  oz.  fine  gold. 

Heading  assay,  sand,  2.4  oz.gold;  tailing  assay,  0.27  oz.  gold. 

Heading  assay,  slime,  2.065  oz.  gold  ;  tailing  assay,  0.1425 
oz.  gold. 

SUMMARY. 

Recovered  from  bullion 230 . 0  oz. 

Recovered  from  concentrate    19.1   ' 

Indicated  recovery  from  sand 102  .2  " 

Indicated  recovery  from  slime 27  .7   ' 


Total  gold 379 . 0  oz. 

Loss  in  sand  residue 13.0  oz. 

Loss  in  slime  residue 2  . 05" 

Assay  of  ore,  per  ton 6 . 23" 


Total  gold  in  ore   394 . 05  oz. 

Extraction 96 . 2% 

In  the  above  statement  it  should  be  noted  that  the  recovery  from  sand 
and  slime  is  indicated  only  on  the  basis  of  careful  sampling  and  assaying, 
as  it  was  not  practicable  to  make  a  cyanide  clean-up  from  so  small  a  lot. 

In  reference  to  the  oxidized  Goldfield  ores,  it  may  be  stated 
that  they  are  peculiarly  adapted  to  milling.  The  gold  is  free, 
but  most  of  it  is  so  extremely  fine  that  it  does  not  readily  am- 
algamate, and  a  complete  cyaniding  equipment  for  handling  both 
sand  and  slime  is  absolutely  essential. 

The  sulphide  ore  at  the  Combination  mine  yields  to  a  some- 
what different  treatmenc,  in  which  elaborate  preliminary  concen- 


36  RECENT  CYANIDE  PRACTICE. 

tration  is  the  chief  feature,  followed  by  cyaniding.  The  small 
quantity  of  concentrate  produced  from  the  oxidized  ore  will  be 
treated  by  cyanide.  The  sulphide  concentrate,  however,  does 
not  yield  to  cyanide,  and  will  no  doubt  eventually  be  chlorinated. 
The  Tonopah  ores,  which  carry  much  silver,  as  well  as  man- 
ganese, a  small  quantity  of  copper  and  other  bases,  were  for  a 
long  time  considered  unsuitable  for  milling.  This  view  is  no 
longer  held  by  the  leading  mine  managers.  Tests  now  being  made 
on  a  representative  Tonopah  ore  at  an  ore  testing  mill  in  San 
Francisco  show  that  an  extraction  of  90%  by  a  combination  of 
concentration  and  cyaniding  may  reasonably  be  expected  in  a 
properly  equipped  plant,  The  ore  in  question  carries  about  25 
oz.  silver  per  ton.  If  we  assume  $15  to  be  the  average  value 
of  the  milling  ore  in  the  district,  an  extraction  of  90%  and  a 
milling  cost  of  $3  per  ton  on  a  40-stamp  basis,  we  have  a  total 
milling  expense  and  loss  of  only  $4 . 50.  This  would  be  slightly 
increased  by  the  cost  of  shipping  the  concentrate ;  but  even  then 
the  cost  would  be  sufficiently  low  to  discourage  shipping  and 
smelting.  And  if  the  high-grade,  ore  of  Goldfield  can  be  more 
profitably  milled  than  smelted,  then  the  same  rule  should  apply 
to  the  Tonopah  ores.  Indeed,  every  present  indication  points  to 
the  distinct  advantage  of  milling  over  smelting  as  applied  to  the 
silicious  gold  and  silver  ores  of  this  whole  new  district;  and  with 
the  development  of  a  better  water-supply  for  milling  purposes 
there  is  no  reason  why  every  property  of  any  consequence  in 
southern  Nevada  should  not  have  its  own  independent  reduction 
plant. 


RE-GRINDING 

(Editorial,  April  7,  1906) 

It  is  likely  that  the  tube-mill  and  the  Chilean  mill  will  be 
close  rivals  as  devices  for  re-grinding  the  product  of  the  stamp- 
mill.  At  Johannesburg,  for  instance,  among  other  installations 
of  tube-mills,  two  18-ft.  tubes  have  just  been  erected  at  the  Fer- 
reira  mill;  one  of  these  was  started  running  on  January  11.  This 
mill  is  re-grinding  the  spitzlutten  discharge  from  a  120-stamp  mill 
that  is  crushing  through  a  22-mesh  light  screen  and  giving  a 
duty  of  about  six  tons  per  stamp  per  24  hours.  About  250  tons 
of  product  per  day  is  passing  through  the  tube-mill.  After  leaving 
the  tube-mill,  the  pulp  passes  over  four  shaking  amalgamated 
plates,  where  about  60  ounces  of  amalgam  per  day  are  caught 
from  the  daily  scrapes  and  from  black  sand  caught  on  the  plates. 
Before  starting  the  tube-mill,  the  custom  was  to  collect  from  the 
spitzkasten  about  10  per  cent  of  concentrate  averaging  14  dwt. 
per  ton.  This  was  given  a  three  weeks'  treatment  with  cyanide, 
which  brought  the  gold  in  the  residue  down  to  about  2.5  dwt. 
Now  only  two  products  are  being  made  :  Sand,  representing 
70  per  cent  of  the  mill-tonnage,  and  slime  representing  30  per 
cent.  The  total  residue  from  the  company's  works  before  starting 
tube-mills  averaged  t.06  dwt.,  now  they  have  come  down  to  0.6 
dwt.,  and  the  manager  expects  to  do  better.  The  following  figures 
in  the  use  of  shaking  amalgamated  plates  in  this  mill  during  1905 
will  be  of  interest:  There  are  24  of  these  plates  running  below 
the  ordinary  fixed  plates  at  the  batteries;  during  the  year  there 
was  collected  from  these  plates  16,028  ounces  of  amalgam;  78 
per  cent  of  this  total  was  recovered  from  dressing  the  plates  and 
22  per  cent  from  steaming  them;  the  total  fine  gold  obtained 
was  4,808  ounces,  valued  at  $97,941,  less  cost  of  running  and 
maintenance  of  plates,  namely,  $5,683;  that  is,  $92,258  repre- 
sents additional  profit  to  the  mill. 

In  Mexico,  a  Chilean  mill  fed  with  a  product  that  had  passed 
a  2J-mch  grizzly,  reduced  18  tons  per  day  at  one  operation,  so 
that  20  per  cent  was  between  100  and  200-mesh  fineness,  while 
over  77  per  cent  passed  200-mesh.  With  a  10  to  1  dilution  and  a 
consumption  of  12  horsepower, this  mill  ran  for  18  months  without 


38  RECENT  CYANIDE  PRACTICE. 

stopping  for  repairs.  It  cost  $4,000  at  Pachuca  and  did  the 
work  described  for  23  cents  per  ton.  Chilean  mills  have  long  been 
in  use  at  Pachuca,  for  they  are  legitimate  descendants  of  the  arrastre; 
nevertheless,  even  the  Spanish  engineers  at  that  ancient  mining 
centre  are  using  Abbe  tube-mills,  so  that  it  is  evident  that  we 
should  soon  be  in  possession  of  valuable  data,  secured  by  making 
trustworthy  tests  between  the  various  machines  employed  for 
re-grinding. 


IRON  V.  WOOD  FOR  CYANIDE  LEACHING 

VATS 
BY  FRANCIS  L.  BOSQUI 

(April  14,  1906) 

The  following  facts  in  regard  to  iron  and  redwood  leaching 
vats  for  the  cyanide  process  will  determine  which  type  is  best 
to  use  in  a  given  locality. 

In  warm  countries,  where  the  winters  are  not  severe  enough 
to  require  housing  the  plant,  the  iron  vat  is  to  be  preferred. 
Iron  vats  are  more  expensive  in  first  cost  and  erection  than  red- 
wood ;  they  are  also  more  expensive  to  maintain,  owing  to  the 
necessity  of  frequent  coating  to  protect  both  the  iron  and  the 
cyanide  solutions.  They  must  be  set  up  with  special  care  and  sub- 
jected to  water-tight  test,  as  leaks  are  difficult  to  stop,  especially 
in  the  bottom,  after  the  filter  has  once  been  laid.  A  serious  ob- 
jection, not  generally  recognized,  is  the  lack  of  rigidity  of  iron 
vat's  when  under  pressure  of  a  charge  of  ore,  and  the  tendency 
of  the  periphery  to  shift  from  the  line  of  the  true  circle.  This 
shifting  or  bulging  will  take  place  during  the  filling  or  after  solu- 
tion is  applied,  and  is  due  to  the  charge  not  being  uniform  in  dens- 
ity and  of  varying  pressure  at  different  points.  Such  a  variation, 
with  the  consequent  yielding  of  the  iron,  will  oftentimes  produce 
cracks  throughout  the  charge  of  sand.  This  prevents  uniform 
percolation  and  is  a  serious  matter.  It  can  be  prevented,  however, 
in  great  measure  by  using  sufficiently  heavy  material  and  re- 
inforcing the  vats  with  bands  of  angle  iron. 

The  redwood  vat  is  perfectly  rigid,  and  is  much  cheaper 
in  first  cost  and  maintenance  than  the  iron  vat.  It  does 
not  require  as  frequent  coating  with  protective  paint.  There  is 
a  popular  prejudice  against  wooden  vats  owing  to  their  alleged 
greater  liability  to  leakage,  and  their  absorption  of  values.  The 
leakage  may  be  prevented  by  good  workmanship  in  setting  up 
the  vat.  The  redwood  leaching  vats  at  the  Smuggler- Union 
cyanide  plant  in  Colorado  are  40  feet  in  diameter,  and  are  abso- 
lutely tight  ;  and  I  am  quite  positive  that  the  same  may  be  said 
of  the  large  54-ft.  vats  at  the  Homestake.  Rare  cases  have  been 
reported  of  losses  from  absorption.  I  investigated  this  point 


40  RECENT  CYANIDE  PRACTICE. 

several  years  ago.  The  results  of  the  tests  made  on  that  occa- 
sion are  quoted  herewith  from  my  article  in  The  Engineering  and 
Mining  Journal  of  Febuary  26,  1898. 

A  piece  of  redwood  5  ft.  2  in.  long  and  2J  in.  thick  was  sub- 
merged for  three  weeks  in  a  gold  solution  at  Bodie.  Weighing 
before  and  after  submersion  showed  an  absorption  of  2f  Ib.  in  80 
hr.,  equal  to  22%  of  the  original  weight.  Assuming  that  a  vat 
weighing  six  tons  would  absorb  as  much  as  50%  of  a  $5  cyanide 
solution,  the  absorption  would  amount  to  three  tons,  or  $15 — an 
almost  imperceptible  loss  in  a  plant  treating  several  thousand  tons 
per  month. 

Another  way  to  account  for  loss  of  gold  by  absorption  is  to 
assume  that  the  absorption  is  cumulative— that  is,  in  a  leaching 
vat  submitted  to  intermittent  contact  with  solution,  the  gold  is  de- 
posited in  the  wood  by  a  series  of  partial  evaporations.  To  deter- 
mine which  was  accompanied  by  the  greater  loss  by  absorption- 
continuous  or  intermittent  contact — and  whether  either  was  re- 
sponsible for  any  considerable  loss,  the  following  tests  were  made  : 

First  series  (continuous  contact). 

(a)  A    piece    of    dressed    redwood,    thoroughly    seasoned, 
weighing  2  Ib.  2  oz.  and  exposing  180  sq.  in.  of  surface,  was  sub- 
merged   for    three    weeks    in     a    solution    carrying    an    average 
of  $5  per  ton  in  gold.     The  wood  was  then  taken  out  and  dried, 
and  reduced  to  charcoal  in  a  clean  solder  stove  and  further  reduced 
to   ash   in   a   new   assay-muffle.     The.  ash   was   carefully   fluxed, 
cupeled,  and  the  button  weighed,  with  the  following  results,  sil- 
ver being  valued  at  50c.  per  ounce: 

Gold.        Silver.  Total 

Actual  absorption mg.     1 . 65            2.75  4  . 40 

Absorption  per  ton  of  wood grams     1 . 552         2 . 588  4.14 

Value  absorbed  per  ton  of  wood $1 . 03  $0 . 04  $1 . 07 

(b)  A  piece    of   seasoned   dressed   pine    weighing  3  Ib.  and 
exposing  180  sq.  in.  of  surface  was  submerged  at  the  same  time 
as  the  redwood  and  subjected  to  the  same  conditions  : 

Gold.        Silver.  Total. 

Actual  absorption    mg.      1.7  2.6  4.3 

Absorption  per  ton  of  wood grams     1 . 133          1  . 733  2 . 866 

Value  absorbed  per  ton  of  wood $0 . 75  $0 . 02  $0.77 


IRON  v.  WOOD  FOR     LEACHING  VATS.  41 

(c)  A  piece  of  rough  pine  weighing  2  Ib.  7  oz.  and  exposing 
144  sq.  in.  of  surface  was  taken  from  the  bottom  of  a  discarded 
screen-frame,  which  had  been  constantly  and  directly  exposed 
to  a  strong  solution  (averaging  $5  per  ton  in  gold)  for  a  period 
of  eight  months,  and  again  for  a  period. of  four  months  : 

Gold.  Silver.       Total. 

Actual  absorption mg.     9.5  10.8  20 . 3 

Absorption  per  ton  of  wood grams     7  .  794  8  . 86  16  . 654 

Value  absorbed  per  ton  of  wood $5 . 18  $0 . 14  $5 .32 

Second  series  of  tests    (intermittent  contact). 

(a)  A  piece  of  dressed  redwood  weighing  2  Ib.  7  oz.  and    ex- 
posing 180  sq.  in.   of  surface  was  subjected  to  intermittent  sub- 
mersion in   a   strong  gold   solution   for  three   weeks.     The   piece 
was  left  in  the  liquid  for  16  hr.  in  24,  and  then    removed    and 
dried  in  the  sun  for  the  other  eight  hours  : 

Gold.        Silver.  Total. 

Actual  absorption mg.     4.8  2.1  6.9 

Absorption  per  ton  of  wood grams     3  .  657          1.6  5  . 257 

Value  absorbed  per  ton  of  wood $2.43  $0 . 02  $2.45 

(b)  Two  pieces  of  rough  pine,  weighing  together  3  Ib.  4  oz. 
and  exposing  each   160  sq.  in.  of  surface,  were  taken  from  near 
the  top   of  the   disused  screen-frame   from  the   gold  tank.     This 
portion   of  the    frame    had   been   alternately   exposed   and   dried 
for  12  months,  and  was  probably  about  one  half  of  the  time  under 
solution  : 

Gold.        Silver.  Total. 

Actual  absorption mg.     6.7  13.7  20 . 4 

Absorption  per  ton  of  wood grams     4.122          8 . 429  12  . 551 

Value  absorbed  per  ton  of  wood $2  .  74  $0.13  $2  . 87 

It  may  be  noted  that  the  portion  of  the  screen-frame  subjected 
to  long  continuous  submersion  showed  the  highest  absorption — 
$5.32  per  ton  of  wood — and  that  the  piece  of  redwood  exposed 
intermittently  to  solution  for  three  weeks  indicated  almost  the 
same  degree  of  absorption  as  the  top  portion  of  the  screen-frame 
exposed  for  several  months. 

The  indications  are  that  in  no  case  would  the  absorption  be 
much  of  a  factor  in  gold  losses,  even  in  a  vat  of  unprotected 
surface. 


THE  ASSAY  OF  CYANIDE  SOLUTIONS 

BY  WILLIAM  MAGENAU 

.  (April  14,  1906) 

About  a  year  ago  I  had  occasion  to  search  for  an  extra  rapid 
method  for  determining  gold  in  cyanide  mill  solutions,  to  be  used 
in  controlling  the  operations  of  an  agitation  plant  which  handled 
charges  of  100  tons  each.  The  process  involved  special  chemical 
treatments,  and  washing  by  decantation;  and  a  quick  solution- 
assay  was  imperative  right  through.  As  a  basis,  I  gathered  from 
text -books  and  files  of  the  technical  press  all  suggestions  along 
this  line,  and  tried  but  a  few  before  finding  one  which,  with 
some  modifications,  answered  well. 

It  may  interest  cyaniders  to  know  this  method,  especially 
as  they  may  have  had  the  same  discouraging  experience  as  I  had 
with  the  method  as  published.  It  was  described  in  The  Engineering 
and  Mining  Journal  of  March  28,  1903,  by  Alfred  Chiddey;  in 
substance  it  was  as  follows  :  Add  to  four  assay-tons  (or  more) 
of  the  solution  10  c.c.  of  10%  solution  of  lead  acetate;  then  four 
grams  zinc  shavings;  boil  a  minute;  add  20  c.c.  HC1  (strong). 
When  action  has  ceased,  boil  again  and  decant  from  the  ball  of  spon- 
gy lead  which  has  been  compacted  a  little  with  a  glass  rod,  and  wash 
same  by  decantation.  Transfer  to  a  piece  of  filter-paper,  roll 
into  a  compact  ball,  and  place  (without  drying)  on  a  hot  cupel 
in  the  muffle. 

Mr.  Chiddey  states  that  a  result  can  be  obtained  in  25  minutes, 
which  I  failed  to  confirm.  It  is  certainly  the  experience  of  most 
of  us  that  it  requires  several  times  that  length  of  time  to  bring 
four  assay-tons  (120  c.c.)  of  solution  twice  to  a  boil,  to  dissolve 
four  grams  Zn  in  HCl,  to  conduct  a  cupellation,  then  part  and 
weigh,  to  say  nothing  of  manipulation.  But  far  from  making  any 
speed  records,  I  could  not  get  the  method  to  work  at  all,  following 
the  scheme  to  the  letter.  Instead  of  the  lead  coming  down  spongy, 
it  was  finely  divided  and  showed  no  tendency  to  agglomerate, 
and  had  to  be  filtered  out  to  collect  it  at  all,  which  it  was  the 
very  merit  of  the  proposed  method  to  avoid.  But  the  precious 
metals  were  perfectly  precipitated,  and  realizing  the  advantages 


THE  ASSAY  OF  CYANIDE  SOLUTIONS.  43 

of  the  scheme,  I  experimented  with  other  proportions  of  reagents 
than  those  given  and  got  good  results  from  the  following  : 

Take  a  large  beaker  (about  600  c.c.  capacity)  five  or  ten  assay- 
tons  of  solution,  and  if  it  is  very  weak  in  KCy  add  enough  of  strong 
pure  solution  to  bring  it  up  to  about  0.5%  strength.  Add  10 
c.c.  of  a  10%  solution  of  lead  acetate,  slightly  acidified  with  acetic 
acid  (12  c.c.  if  10  assay-tons  were  taken)  ;  then  add  by  rough 
measure  on  the  point  of  a  spatula  between  0 . 3  and  0 . 4  gram 
(not  more)  of  zinc  dust,  this  being  sufficient  to  precipitate  all 
lead  present  and  leave  an  excess  of  zinc  to  act  on  Au  and  Ag. 
Stir  and  bring  to  a  boil  ;  then  add  15  c.c.  strong  HC1  and  leave 
on  the  hot  plate  until  excess  Zn  is  dissolved  and  lead  has  gath- 
ered into  a  sponge.  This  will  take  but  a  few  minutes,  and  the 
assay  should  then  be  taken  from  the  heat,  else  the  lead  will  begin  to 
dissolve.  Now  gather  the  lead  a  little  with  a  glass  rod  whose 
end  has  been  flattened  while  hot,  or  with  the  fingers  encased  in 
a  rubber  cot,  decant  rapidly,  wash  by  decantation  two  or  three 
times  with  large  quantities  of  water,  pick  up  the  lead  (which 
should  be  soft  and  strongly  inclined  to  stick  together  when 
pressed)  in  the  fingers  and  compress  it  into  a  ball  which  place 
upon  a  piece  of  lead  foil  1^  in.  square.  (Using  filter-paper 
instead  of  lead  foil,  the  spongy  lead  is  apt  to  separate  in  the  cupel.) 
Fold  up  in  such  a  way  as  to  leave  an  egress  for  steam,  and  drop 
into  a  hot  cupel  in  the  muffle,  having  first  added  a  bit  of  silver, 
if  the  assay  is  for  gold  only. 

The  solution  on  which  this  method  gave  excellent  results,  and 
checked  perfectly  with  the  old  evaporation  methods  in  minimum 
time,  carried  about  0.075%  KCy  and  from  nothing  to  one 
ounce  Au  per  ton  with  almost  no  Ag.  It  is  possible  that  Mr. 
Chiddey's  method,  as  published,  works  better  on  other  solutions, 
though  it  is  not  clear  why  so  much  as  four  grams  zinc  need  be  used, 
taking  a  long  time  to  dissolve  when  one-tenth  as  much,  in  the  shape 
of  'dust,'  is  ample.  Perhaps  different  proportions  of  reagents  will 
be  necessary  to  suit  each  case,  but  operators  will  find  it  worth  a 
little  experimenting  to  secure  a  method  which  involves  no  filtra- 
tion, no  fusion  nor  scorification,  is  accurate  and  rapid, 
easily  performed  and  equally  suited  to  large  batches  and  single 
assays. 

The  method  may  be  used  without  application  of  heat,  as  the 
precipitation  of  precious  metals  is  perfect  in  the  cold,  but  the  lead 


44  RECENT  CYANIDE  PRACTICE. 

does  not  agglomerate  well  and  the  excess  zinc  takes  longer  to 
dissolve.  When  done  this  way,  the  precipitated  lead  (plus  Au 
and  Ag)  must  be  filtered  out  and  the  paper,  unwashed  and  still 
wet,  rolled  up  in  a  piece  of  lead  foil  about  two  inches  square  and 
dropped  into  a  hot  cupel. 

It  may  be  of  further  interest  and  a  convenience  to  have  the  list 
of  methods  which  I  gathered,  chiefly  from  the  American  techni- 
cal journals  of  the  past  eight  years;  cyanide  chemists  may  be 
encouraged  thereby  to  give  them  a  trial,  and  let  the  profession 
know  the  results.  Gold  determination  has  been  the  chief  concern, 
but  these  methods,  except  where  noted  to  the  contrary,  may  be 
used  equally  well  for  silver. 

I.        METHODS      INVOLVING      CRUCIBLE      FUSION      OR     SCORIFICATION 
BEFORE    CUPELLATION. 

1.  Evaporation  in  a  lead-foil  tray,  either  direct,  or  after  con- 
centration to   small  bulk  in  a  porcelain  dish,  the  finish  to  be  con- 
ducted at  a  very  low  heat.     The  tray  is  rolled  up  so  as  to  enclose 
the   residue,    and   is   scorified   with   test   lead   before   cupellation, 
parting,  and  weighing.     With  small  charges   (say  one  assay-ton) 
of    solution    carrying    only    small    amounts    of    dissolved    matter, 
the  scorification   can   be   omitted.       A   variation   of  the  method 
which  avoids  the  lead  tray,  is  to  sprinkle  into  the  charge  of  solution 
(in  a  porcelain  dish)  20  grams  litharge,  in  such  a  way  as  to  cover 
the  bottom;  then  evaporate  to  dryness,   and  scrape  the  residue 
with  a  spatula  into  a  crucible  containing  10  grams  sodium  bicar- 
bonate, five  grams  borax  glass,  and  one  gram  flour  or  argol.     The 
dish  can  be  thoroughly  cleaned  by  moistening  with  dilute  nitric 
acid  and  mopping  out  with  small  pieces  of  filter-paper  which  are 
added  to  the  crucible.     Fusion  results  in  a  lead  button,  which  is 
cupelled,    etc.      The    evaporation    method   is   the   oldest   in   use, 
and   when   carefully   done  is   accurate.     It   involves   much   time, 
but  little  and  simple  manipulation. 

2.  Precipitation    as    Sulphide  in   Acidified  Solution. — This  is 
given  in  The  Engineering  and  Mining  Journal,  November,  1898,  by 
Henry  Watson,  and  is  stated  to  be  quick,  accurate,  and  economi- 
cal. 

Acidify  five  or  ten  assay-tons  solution  with  HC1  and  heat  to 
boiling;  while  boiling,  add  a  solution  of  two  grams  lead  acetate 


THE  ASSAY  OF  CYANIDE  SOLUTIONS.  45 

and  pass  a  current  of  sulphuretted  hydrogen  until  all  Pb  is  precip- 
itated. Allow  to  cool  a  little  while,  still  passing  H2S,  then  filter, 
precipitate,  dry,  and  reduce  to  a  lead  button  by  scorification 
with  lead  test  or  fusion  with  fluxes  in  a  crucible;  cupel,  etc. 

3.  Precipitation  by  Cement  Copper  in  Acid  Solution. — Albert 
Arents  in  Trans.  A.  I.  M.  E.,  Vol.  XXXIV,  p.  182:  Add  a  few  cubic 
centimetres  H2SO4  to  six  or  eight  assay-tons  of  solution,  stir  well, 
and  add  one  gram  (not  much  more  nor  less)  of  commercial  cement 
copper.     Boil  hard  for  10  min.     Filter  through  a  large  gray  paper 
without  washing.     Place  in  an  assay  crucible  one-third  of  a  flux- 
ing mixture  consisting  of  30  grams  litharge  with  usual  amounts 
of  soda,   borax,  and  reducer,   and  on  the  drained  filter,   another 
third.     Then  pick  up  the  filter,  tuck  it  into  the  crucible,  and  cover 
with  the  remaining  third  of  flux.     Now  fuse,  cupel,  etc.     Instead 
of  cement  copper,  a  solution  of  CuSO4  may  be  added  and    then 
some   aluminum   foil.     Boiling   the   assay   for   some   time    brings 
down  the  copper.     The  aluminum  foil  should  be  added  to  the  fusion 
of  filter. 

4.  Precipitation  by  Silver  Nitrate. — Credited  to  A.  Crosse  on 
p.  161  of  Gaze's  book  on  the  'Cyanide  Process.'     Add  an  excess  of 
silver  nitrate  solution ;  filter  and  wash ;   dry  filter  and  either  scorify 
it  with  test-lead  after  incineration,  or  fuse  with  fluxes  in  a  crucible, 
cupelling    the    resultant    lead    button.     This    method,    of   course, 
can  be  used  for  Au  only.     Gaze  also  gives  a  modification  of  this 
which  employs  a  bichromate  of  potash  indicator  to  determine  when 
there  is  an  excess  of   AgNO3,  and  directs  that  a  few  grams  of  zinc- 
dust  be  added  besides.     After  stirring  well,  an  excess  of  H2SO4 
is  added.     Then  filter  and  wash,  dry,  fuse,  and  cupel;  or  the  incine- 
rated filter  may  be  cupelled  direct  when  wrapped  in  lead-foil. 
Mercuric  chloride  may  be  used  instead  of  silver  nitrate. 

5.  Precipitation  by  Copper  Salt. — Maurice  Lindemann  in  The 
Engineering  and  Mining  Journal,  July  1,  1904.     Heat  10  assay-tons 
until  quite  hot ;  add  ammoni  ,cal  copper  nitrate  solution  to  a  per- 
manent blue;  carefully  acidify  with  H2SO4;  stir  and  filter  imme- 
diately.    Dry  and  incinerate  the  filter,  fuse  or  scorify,  cupel,  etc. 
Some  chemists  claim  this  method  will  not  work  on  foul  solutions. 

Grant  D.  Miller  in  The  Engineering  and  Mining  Journal,  June  23, 
1904,  treats  34.3  assay-tons  (one  litre)  of  solution  in  a  two-litre 
flask  with  one  to  two  grams  copper  sulphate.  After  shaking  well, 


46  RECENT  CYANIDE  PRACTICE. 

add  10  to  15  c.c.  strong  HC1  and  shake  well  again.      Filter,  dry, 
and  incinerate,  fuse,  cupel,  etc.,  as  before. 

6.  Precipitation  by  Zinc  Shaving  or  Dust  in  Acid  Solution. — 
H.  L.   Durant  in  Jour.  Chem.  &  Met.  Soc.  of  S.  A.,   December, 
1902.     Place  a  large  measured  bulk  of  solution  in  a  flask,  acidify 
strongly  with  H2SO4  and  bring  to  a  boil.     Add  30  grams  zinc 
shaving,  about  five  grams  at  a  time,  waiting  with  each  addition 
until    all    that    previously    added    is    dissolved.     Keep    solution 
strongly  acid  throughout.     When   all   has   been   added  and   dis- 
solved,  put  in   one  gram   precipitated   silicia  to   collect   floating 
matter,   filter  through   double  papers,   dry  and  char  the  papers 
on  a  scorifier,   and  then  add  test-lead,  scorify  and  cupel.     This 
method  can  be  used  for  Au  only,  since  Ag  dissolves  as  sulphate. 

A  much  more  practical  method  is  used  in  the  Black  Hills  and 
elsewhere.  To  eight  assay-tons  of  solution  are  added  enough 
silver  nitrate  solution  to  furnish  inquartation  for  gold;  then  0.33 
to  0.5  gram  zinc-dust  and  sufficient  H2SO4  to  react  completely, 
say  5  to  10  c.c.  Stir  a  little  and  filter  through  an  ordinary  paper, 
dry,  incinerate,  and  fuse  in  a  crucible  with  litharge  and  reducer 
for  a  lead  button,  which  is  cupelled,  etc. 

7.  Precipitation  by  Emulsion  of  Zinc-Dust  in  Lead  Acetate. — 
This  method  was  used  in  some  large  mills  in  Colorado  a  few  years 
ago,  but  I  am  unable  to  give  more  than  a  bare  outline,  and  do  not 
know  how  it  will  work  out.     Make  a  thin  paste  of  zinc-dust  in  a 
strong  solution  of  lead  acetate  and  add  about  8  c.c.  of  this  to  20 
or  30  assay-tons  of  solution.     Agitate  and  let  stand  for  a  time. 
Filter  and  add  dilute  H2SO4  to  the  filter  and  wash.     Dry,  filter, 
incinerate,  fuse  with  litharge  (or  scorify  with  test-lead) ,  and  cupel, 
etc.     This  is  virtually  the  same  as  suggested  for  cold  treatment 
of  the  modified  Chiddey  scheme,  already  described,  though  differing 
in  manipulation. 


II.       METHODS     WHICH     GATHER     PRECIOUS     METALS     IN     LEAD     THAT 
CAN    BE    CUPELLED    DIRECT. 

1.  Evaporation  either  conducted  entirely  in,  or  finished  in,  a 
lead-foil  tray,  when  solution  is  comparatively  small  in  amount 
(one  to  two  assay  tons)  and  contains  only  small  amounts  of  dis- 
solved salts  [see  I  (1)]. 


THE  ASSAY  OF  CYANIDE  SOLUTIONS.  47 

2.     Chiddey  Method,  or  modification  described.     This  seems  to 
be  really  the  only  method  properly  and  exclusively  in  this  class. 


III.     COLORIMETRIC  METHODS   (for  gold  only). 

1.  By  Stannous  Chloride  Following  Precipitation  and  Re-solu- 
tion of  Gold. — Prister  in  Jour.  Chem.  Met.  &  Min.  Soc.  of  S.  A., 
December,   1903,  gave  a  method  which  would  seem  too  long  for 
practical  use.     He  adds  to  the  acidified  and  boiled  solution  under 
assay  a  few  cubic  centimetres  of  a  10%  solution  of  CuSO4  con- 
taining 20%   NaCl,  and    acidified    with    acetic  acid  after    having 
been  boiled  10  min.  with  copper   shaving   and  cooled.     The    pre- 
cipitate resulting  from  addition  of  this  reagent  is  filtered  out  and 
re-dissolved  in  a  KCy  solution,  and  to  this  is  added  a  half  gram 
of  zinc-dust.     After  agitation  for  a  few  minutes,  this  is  filtered  off 
and  treated  on  the  filter  with  dilute  HC1.     Treatment  of  the  same 
filter  with  aqua  regia  (minimum  quantity)  dissolves  the  gold,  and 
in  the  solution  an  excess  of  strong  stannous  chloride  solution  gives 
the  'purple  of  Cassius'  test,  which  may  be  compared  with  standards. 

Later  Prof.  Prister  published  a  simplification  of  this  scheme 
which  reads  better.  The  solution  under  test  is  brought  up  to  one 
per  cent  KCy.  To  234  c.c.  (eight  assay-tons)  add  one  gram 
zinc-dust  and  heat  to  boiling.  Filter;  pour  on  filter  20  c.c.  hot  10% 
H2SO4  repeating  until  all  the  zinc  is  dissolved.  Treat  residue  on 
the  filter  with  10  c.c.  hot  aqua  regia  (6HC1,  2HNO3,  6  water),  pass- 
ing the  10  c.c.  repeatedly  through  same  filter  at  aboil.  Collect  in  a 
test  tube,  cool  and  add  a  "few  drops"  stannous  chloride  as  before. 
Prof.  Prister  does  not  say  how  he  avoids  disintergration  of  the  filter 
by  action  of  hot  aqua  regia.  From  work  I  have  done  with  'purple 
of  Cassius'  tests  on  aqua  regia  solutions  of  gold,  good  and  con- 
stant colors  cannot  be  obtained  unless  the  acids  are  present  in 
small  amounts  and  a  large  excess  of  stannous  chloride  is  used. 

2.  With  Stannous  Chloride  Without  Previous  Precipitation  of 
Gold. — Henry  R.  Cassel  has  given  a  promising  quick  test  as  follows: 
To  10  c.c.  of  solution  in  a  test-tube  is  added  0.5  gram  potassium 
bromate,    then    pure    strong    H2SO4    slowly    until     action  starts. 
When  action  has  ceased,  add  drop  by  drop  a  strong  solution  of 
stannous  chloride,  until  the  solution  is  just  colorless.     In  about 
half  a  minute  the  purple  color  will  form.     Mr.  Cassel  says  the  test 


48  RECENT  CYANIDE  PRACTICE. 

can  be  performed  in  three  minutes,  and  is  delicate  to  a  value 
of  a  few  cents  per  ton  of  solution.  By  concentrating  by  evapora- 
tion very  low-grade  solutions  or  diluting  those  too  strong  in  gold, 
this  method  may  apply  to  a  wide  range. 

He  also  used  other  agents  than  potassium  bromate  as  a  destroy- 
er of  the  interference  of  cyanogen,  namely,  potassium  chlorate  arid 
HC1,  or  H2SO4,  with  long  boiling;  potassium  bromide  followed  by 
sodium  peroxide  and  neutralization  with  H2SO4,  after  which  HC1, 
and  stannous  chloride  are  added  to  give  the  color.  This  last  acts 
well.  Another  scheme  is  to  add  to  the  solution  one-third  its 
bulk  of  strong  ammonia  and  then  neutralize  with  strong  H2SO4. 
The  solution  will  then  react  with  stannous  chloride.  For  quanti- 
tative work,  standards  must  be  prepared,  and  to  make  these 
durable  is  a  great  difficulty  of  the  method.  Considerable  skill 
is  also  needful. 


IV.       ELECTROLYTIC    METHODS. 

1.  Deposition  on  Lead. — In  Trans.  Inst.  of  Min.  &  Met.,  May 
16,  1905,  F.  B.  Stevens  gives  a  method  which  does  not  appear  to 
possess  any  advantages  over  the  chemical  processes  in  points 
of  time,  convenience,  or  accuracy.  Fourteen  to  twenty  assays  of 
10  assay-tons  each  (292  c.c.)  are  electrolyzed  by  current  from 
110- volt  lighting  main  for  four  hours,  using  a  lead-foil  cathode 
of  cylindrical  shape  2^  in.  high  and  1  in.  diam.,  with  three  V 
notches  around  the  bottom,  and  a  large  iron  nail  for  anode.  To 
each  assay  12  to  15  c.c.  of  strong  ammonia  is  added.  The  cathode 
should  be  covered  with  one-half  inch  of  solution.  Twenty  assays 
give  just  right  resistance,  and  with  less  than  14,  electric  lamps 
must  be  put  in  circuit.  With  a  current  varying  from  0.06  to  1.2 
ampere,  according  to  foulness  of  the  solution,  the  gold  comes 
down  bright.  The  cathode  is  washed,  dried,  rolled  up.  and  scorified 
with  test-lead  before  cupelling. 

The  only  figures  given  for  completeness  of  precipitation  state 
that  a  solution  carrying  $10  to  $15  in  gold  will  be  cleaned  to  about 
lOc.  in  four  hours.  If  this  is  the  best  that  can  be  done,  the  method 
is  not  applicable  to  low-grade  solutions.  It  would  seem  that 
cupellation  of  the  cathode  might  be  made  without  preliminary 
scorification. 


THE  ASSAY  OF  CYANIDE  SOLUTIONS.          .    49 

It  will  be  noticed  that  for  most  of  the  above  methods  charges 
of  10  assay-tons,  or  less,  are  recommended,  which  will  perhaps 
seem  inadequate  to  some,  particularly  South  African  operators. 
Most  English  authorities  (as  Julian  and  Smart)  insist  that  only 
very  large  charges  be  used.  The  authors  named  say  not  less 
than  30  assay-tons  and  up  to  200.  In  America  balances  can 
readily  be  purchased  which  are  sensitive  to  0.01  mg.,  or  even 
one-fourth  of  this.  Taking  the  former  figure,  200  assay-tons 
would  give  gold  results  accurate  so  far  as  the  weighing  is  con- 
cerned, to  0.001  per  ton.  What  conceivable  use  such  a  degree 
of  precision  can  be  is  not  stated.  Even  30  assay-tons  would  weigh 
down  to  0.007,  which  is  far  finer  than  available  methods  of  sampling 
and  measuring  ore  and  solution  tonnages  justify.  Ten  assay-tons 
give  a  bead  weighable  to  0.02,  and  nothing  besides  investigation 
work  need  be  concerned  with  less  than  this. 


THE  ASSAY  OF  CYANIDE  SOLUTIONS 

(April  28,  1906) 

The  Editor: 

Sir — Mr.  William  Magenau,  in  your  issue  of  April  14,  mentions 
some  modifications  in  the  method  of  Mr.  Alfred  Chiddey  described 
in  The  Engineering  and  Mining  Journal,  of  March  28,  1903.  I 
have  used  the  same  method  with  somewhat  different  modifications, 
getting  accurate  results  but  consuming  a  much  longer  time.  The 
method,  as  modified,  is  as  follows: 

Take  100  c.c.  of  the  solution  to  be  assayed,  add  7  c.c.  of  £ 
10%  lead  acetate  solution,  then  add  one  gram  of  zinc  shavings 
and  place  on  the  hot  plate.  Heat,  but  not  to  boiling,  until  the  lead 
has  gathered  around  the  pieces  of  zinc.  This  usually  takes  about 
25  minutes.  This  precipitation  being  complete,  20  c.c.  con- 
centrated HC1  is  added  and  the  heating  continued  until  all 
effervescence  has  stopped.  The  lead  is  then  in  such  a  spongy 
condition,  that  by  the  aid  of  a  flattened  glass  rod,  it  can  be  pressed 
into  a  cake  and  the  clear  solution  poured  off.  Wash  the  lead 
twice  and  then  with  the  fingers  press  it  into  a  compact  mass, 
drop  in  a  lead-foil  funnel,  leaving  a  vent  for  escape  of  the  steam, 
place  in  a  hot  cupel  and  proceed  as  in  an  ordinary  cupellation. 
This  latter  operation  consumes  from  25  to  35  minutes;  the  lead 
button  is  ready  for  cupellation  in  about  one  hour. 

I  have  used  this  on  solutions  varying  in  strength  from  0.01% 
KCN  to  0.4%  KCN  and  in  value  from  0.04  to  3  oz.  gold  per  ton. 
I  have  also  used  it  for  the  assay  of  silver  solutions,  but  when  they 
are  rich  the  results  are  lower  than  those  obtained  by  the  evapora- 
tion in  lead  boats. 

The  secret  of  keeping  the  lead  from  breaking  up,  is  not  to 
allow  the  solution  to  come  to  a  boil  at  any  state  of  the  procedure 

NORMAN  C.  STINES. 

Berkeley,  Cal.,  April  23,  1906. 


THE  TREATMENT  OF  DESERT  ORES 

(May  26,  1906)  * 

The  Editor: 

Sir — One  of  the  first  requisites  of  good  criticism  is  that  the 
critic  shall  at  least  give  his  victim  a  fair  hearing.  I  refer  to  cer- 
tain strictures  in  your  issue  of  April  28,  on  a  brief  article  of  mine 
touching  upon  ore  treatment  in  the  Tonopah-Goldfield  district. 
If  unwittingly  I  have  trodden  rough-shod  on  any  of  Mr.  Bertram 
Hunt's  metallurgical  hobbies,  I  am  sorry;  but  before  proffering 
a  formal  apology  I  must  ask  him  to  do  me  the  justice  to  re-read 
my  article,  which  he  so  bluntly  dismisses  and  so  obviously  mis- 
understands. 

In  reference  to  the  necessity  of  amalgamation  at  the  Combina- 
tion mill  at  Goldfield,  I  was  not  undertaking,  as  Mr.  Hunt  infers, 
a  general  discussion  of  the  treatment  "of  oxidized  ores  of  the  desert 
regions  of  Nevada  and  California."  The  classification  of  'desert 
ores'  is  Mr,  Hunt's  own.  It  seems  to  me  a  poor  one,  because  all 
sorts  of  ores  are  found  in  the  desert,  requiring  various  modes 
of  treatment;  and  variations  quite  as  pronounced  are  found  in 
mountainous  regions  and  high  altitudes.  Hard  ores  are  found  in 
the  desert,  as  well  as  soft  ores;  oxidized  as  well  as  sulphide;  and 
any  technical  man  familiar  with  desert  conditions,  especially  those 
observable  at  Tonopah,  Goldfield,  and  Bullfrog,  would  hardly 
fall  into  the  blunder  of  making  so  meaningless  a  classification. 

I  was  not  generalizing  when  speaking  of  ore  treatment  at 
the  Combination  mine.  I  was  plainly  referring  to  a  specific 
case  of  an  unusual  type  of  oxidized  ore,  peculiar  to  a  limited  dis- 
trict. Mr.  Hunt  advocates  dry  crushing  as  applied  to  the  soft 
oxidized  porous  ores  of  the  desert,  under  the  impression,  evidently, 
that  this  is  the  sort  of  ore  found  at  Goldfield,  and  that  it  is  charac- 
teristic of  the  deserts  of  Nevada  and  California.  This  is  an  error 
into  which  others  have  fallen  who  are  not  acquainted  with  the 
southern  Nevada  fields.  The  oxidized  ores  of  Goldfield  are  not 
porous,  and  they  are  not  soft;  in  fact  they  are  extremely  hard. 
The  ore  of  the  Combination  mine  has  been  described  as  a  silicified 
andesite.  It  is  so  hard  and  tough  and  fine-grained  that  selected 
pieces  of  it  have  been  considered  suitable  for  replacing  the  flint 
pebbles  in  the  tube-mill  used  for  re-grinding  the  softer  sulphide 


52  RECENT  CYANIDE  PRACTICE. 

ore.  Some  idea  of  its  hardness  may  be  gathered  from  the  fact 
that  1,300-lb.  stamps,  with  6-in.  drop,  falling  100  times  per  min. 
will,  under  the  best  conditions,  put  only  3  to  3£  tons  per  stamp 
per  day  through  a  12-mesh  wire  screen. 

Mr.  Hunt  bewails  "the  present  fashion  of  putting  in  stamp- 
mills  and  amalgamating  arrangements  followed  by  a  cyanide 
annex,  as  due  solely  to  the  compelling  power  of  custom."  If  such 
is  the  prevailing  practice,  it  is  much  to  be  deplored;  and  I  regret 
it  no  less  than  he.  But  the  allusion  so  papably  insinuates  that  I 
have  offended  in  the  case  of  the  Combination  mill  that  I  hasten 
to  relieve  Mr.  Hunt's  anxiety  on  this  score  by  offering  a  few  facts. 

The  Combination  mill  at  Goldfield  was  not  installed  until 
the  treatment  of  the  ore  had  been  throughly  investigated.  This 
required  about  six  months.  Laboratory  tests  were  confirmed 
by  milling  tests.  Dry  crushing  was  given  a  fair  trial,  but  the 
extraction  in  each  instance  was  poor;  and  after  fifteen  days'  leaching 
with  the  ordinary  strength  of  solution  used  on  gold  ores,  it  was 
still  found  possible  to  pan  from  the  tailing  considerable  quantities 
of  gold  undissolved  by  cyanide.  Several  strengths  of  solution 
were  tried ;  the  ore  was  reduced  to  various  degrees  of  fineness ;  and 
still  dry  crushing  was  not  applicable.  Finally  wet  crushing  under 
stamps,  folio  wed  by  amalgamation,  concentration,  and  cyanidat  ion, 
was  found  to  be  the  proper  treatment,  and  was  adopted.  I  do  not 
propose  to  enter  here  into  the  details  of  treatment,  as  I  am  reserv- 
ing this  for  a  special  article.  But  suffice  it  to  say  that  contrary 
to  Mr.  Hunt's  belief,  the  matter  of  ore  treatment  was  given  a 
thorough  study;  and  we  were  not,  at  least  in  this  instance,  the 
slaves  of  custom. 

In  regard  to  the  recovery  of  gold  on  plates;  I  would  certainly 
advocate  the  use  of  amalgamation  where  as  much  as  50%  of  the 
gold  can  be  so  recovered.  Mr.  Hunt  is  possibly  not  familiar  with 
the  character  of  the  gold  found  in  the  Goldfield  district.  It  is 
fine,  to  be  sure,  as  distinguished  from  the  coarse  gold  of  the  Cali- 
fornia Mother  Lode,  which  yields  such  high  results  to  amalgama- 
tion; but  it  is  not  by  any  means  invisible,  and  most  of  it  can 
be  'panned  out'  in  an  ordinary  miner's  pan.  In  other  words, 
it  is  too  coarse  for  direct  cyaniding  and  too  fine  for  the  best  results 
by  amalgamation.  Moreover,  Mr.  Hunt  has  evidently  not  con- 
sidered the  great  advantage  of  being  able  to  secure  daily  from 
plates  50%  of  the  extraction  obtained  from  $50  ore,  as  compared 


THE  TREATMENT  OF  DESERT  ORES.  53 

with  waiting  for  the  tedious  monthly  or  bi-monthly  clean-up 
in  a  cyanide  plant,  and  his  suggestion  that  amalgamation  be  tried 
after  cyanide  treatment  by  passing  the  tailing  "over  some  amal- 
gamating device,"  while  no  doubt  ingenious,  will  hardly  appeal 
seriously  to  practical  mill-men.  And  what,  let  me  ask,  does  Mr. 
Hunt  propose  to  do  with  the  very  high-grade  concentrate  obtained 
from  this  ore,  which  it  pays  so  well  to  extract  and  ship?  Must 
this  also  be  removed  after  cyanide  treatment  ? 

My  critic's  views  on  this  whole  subject  are  summed  up  in  his 
query,  "As  the  majority  of  these  oxidized  ores  give  a  practically 
complete  extraction  by  direct  cyanide  treatment,  what  is  the 
advantage  of  using  both  amalgamation  and  cyanide  to  recover  the 
same  value?" 

My  answer  is  that  I  do  not  admit  the  correctness  of  Mr.  Hunt's 
premises.  He  is  evidently  an  ardent  advocate  of  dry  crushing; 
and  while  I  did  not  intend  to  prolong  this  discussion  into  a  consid- 
eration of  the  respective  merits  of  the  two  processes,  I  cannot 
refrain  from  mentioning  some  of  the  more  serious  limitations  of 
dry  crushing.  A  few  years  ago  I  was  happily  instrumental  in 
converting  one  of  the  largest  dry-crushing  plants  in  the  West 
(that  of  the  Gold  Road  mine  in  Arizona)  into  a  wet-crushing  mill: 
It  was  an  expensive  and  well-equipped  plant  and  had  been  in  opera- 
tion several  years ;  and  so  far  as  I  could  see,  it  had  been  worked  to 
its  highest  efficiency.  The  extraction  obtained  was  about  80%. 
The  change  to  wet  crushing,  using  Huntington  mills  in  conjunc- 
tion with  the  coarse  rolls  already  installed,  and  Dehne  filter- 
presses  to  handle  the  slime,  raised  the  extraction  10%,  and  con- 
siderably decreased  the  cost  of  treatment.  Amalgamation,  in 
this  case,  was  dispensed  with  altogether,  as  only  about  15%  of  the 
value  could  be  so  recovered.  Two  other  representative  dry-crush- 
ing mills,  one  in  Utah  and  the  other  in  southern  California,  are  now 
considering  the  remodeling  of  their  plants  for  dry  crushing,  after 
obtaining  promising  experimental  results. 

These  projects  and  changes  are  all  based  upon  the  following 
facts,  which  I  believe  will  sooner  or  later  reduce  the  applicability 
of  dry  crushing  to  a  few  rare  and  isolated  cases:  (1)  The  im- 
possibility (from  an  economic  standpoint)  of  reducing  ore  to  a 
sufficient  fineness  to  ensure  the  best  recovery,  without  making 
percolation  prohibitively  slow.  (2)  The  now  generally  accepted 
view  that  the  product  of  any  ore-crushing  mill  must  be  handled 


54  RECENT  CYANIDE  PRACTICE. 

either  as  a  slime,  or  as  classified  sand  and  slime.  The  slime  requires 
short  treatment  with  weak  solutions;  the  sand,  long  contact  with 
stronger  solutions.  Every  modern  mill,  operating  on  a  logical 
basis,  must  handle  its  final  cyaniding  material  as  two  separate 
products. 

Aside  from  the  great  discomfort  to  workmen  in  a  dry-crushing 
mill,  and  the  resulting  well-grounded  prejudice  which  they  have 
against  these  mills,  the  great  fundamental  objection  to  this  type 
is  that  it  is  not  adapted  to  the  requirements  of  the  latest  and  best 
practice  in  cyaniding.  An  exception  to  this  would  be  in  the  treat- 
ment of  a  porous  ore  containing  little  or  no  amalgamable  gold,  and 
requiring  hardly  more  than  breaking,  like  the  ore  formerly  treated 
in  the  old  Mercur  plant,  or  an  ore  which  requires  roasting  before 
cyaniding.  Conditions  so  ideal  for  dry  crushing  are  rare;  at  least 
they  are  not  common  enough  to  affect  the  general  rule  prescribed 
above. 

Mr.  Hunt  mentions,  among  the  objections  to  wet  crushing, 
that  the  moisture  in  the  ore  must  be  displaced,  entailing  a  loss  of 
cyanide.  This  would  be  a  very  serious  matter  indeed  if  there 
were  no  conceivable  objections  to  dry  crushing.  Each  method,  of 
course,  has  its  objectionable  features.  The  discussion  of  so  impor- 
tant a  subject  should  be  undertaken  in  a  fair  and  liberal  spirit; 
the  merits  and  demerits  of  each  process  carefully  weighed;  and 
obviously  the  final  choice  accorded  to  the  method  which  has  the 
preponderance  of  commercial  advantages  as  applied  to  a  particu- 
lar ore.  After  a  careful  study  of  the  two  methods,  and  some 
experience  in  both,  I,  for  one,  am  persuaded  that  the  present 
recognized  need  of  fine  grinding  in  cyanide  work,  and  the  treat- 
ment of  slime  as  a  separate  product,  will  ultimately  reduce  the  field 
of  dry  crushing  to  a  very  limited  scope. 

FRANCIS  L.  BOSQUI. 
San  Francisco,  May  10,  1906. 


NOTES  ON  TUBE-MILLS  AT  EL  ORO,  MEXICO 
BY  CHARLES  BUTTERS 

(May  26,   1906^ 

Foundations. — The  management  of  El  Oro  Mining  &  Railway 
Co.  had  a  good  deal  of  trouble  with  the  foundation  of  one  tube- 
mill,  due  to  improper  setting  of  the  cement.  There  is  a  terrible 
vibration  when  the  mill  is  running.  It  would  be  best  to  make 
the  foundations  10%  heavier  than  the  plans  usually  called 
for,  using  the  very  best  cement,  and  allowing  sufficient  time  to 
set  clear  through  before  the  tube  starts.  Underneath  there 
should  be  a  good  cement  floor  sloping  to  a  gutter  leading  to  the 
cone,  spitzkasten,  pump,  or  wheel,  constituting  the  return  circuit,  so 
that  the  floor  can  be  washed  with  a  hose,  the  washing  being  returned 
with  all  leakage  of  mills  for  re-grinding. 

Rotation. — It  is  important  that  the  tubes  rotate  in  a  direction 
such  as  to  cause  the  thrust  of  the  driving  pinion  to  be  downward 
into  the  pillow-block,  and  not  up  against  the  cap;  the  rotation 
should  be  effected  by  an  open  belt,  if  possible.  If  in  accomplishing 
this  the  mill  runs  backward,  it  is  best  to  reverse  the  spiral  in  the 
feed-throat,  as  the  spiral  is  the  only  thing  that  makes  any  differ- 
ence to  the  direction  of  rotation.  The  spiral  at  the  discharge  end 
can  be  removed  altogether,  as  it  seems  to  be  of  no  practical  value, 
mills  working  just  as  well  without  it,  as  others  with  it  on  the  same 
work. 

Leaks. — A  leak  will  often  start  around  a  bolt  when  it  is  im- 
practicable to  shut  the  mill  down.  If  there  is  a  cement  floor 
it  will  make  no  difference,  or  a  bolt  may  cut  out  entirely.  In  this 
case,  feel  in  the  hole  with  the  finger  and  if  the  liner  is  good,  put  a 
wooden  plug  in  the  hole  until  such  time  as  is  necessary  to  shut  down 
for  more  extensive  repairs.  If  the  leak  occurs  at  the  head  of  the 
mill,  the  sand  will  get  into  gears  and  cut  them  badly.  This  can 
be  obviated  by  putting  a  shield  on  the  gear-wheel  rim,  to  cover 
outside  ends  of  teeth,  by  fastening  (with  cap-screws)  a 
ring  cut  from  sheet-iron  No.  14  or  16  gauge.  This  should,  by 
all  means,  be  done  before  the  mill  is  set  up. 

Feed. — In  case  the  feed-hopper  and  the  pipe  that  enters  the 
mill  come  in  one  piece  (as  they  did  at  El  Oro) ,  cut  the  pipe  off  as 


56  RECENT  CYANIDE  PRACTICE. 

close  to  the  hopper  as  possible,  and  put  in  a  flange  or  sleeve, 
threaded  in  direction,  so  that  the  rotation  of  the  mill  will  not  screw 
it  off.  The  pipe  will  have  to  be  made  a  little  longer  than  the 
piece  cut  off,  as  the  connection  will  necessitate  setting  the  hopper 
further  back,  in  order  to  get  at  the  packing  gland.  There  is  a 
great  deal  of  wear  on  the  pipe.  By  this  means  it  can  be  quickly 
and  easily  replaced.  The  best  packing  to  use  is  f-in.  common 
hose  cut  in  individual  rings.  There  should  be  a  de- watering  cone, 
or  pulp-thickener,  directly  over  the  feed-hopper,  to  get  the  pulp 
as  thick  as  possible  for  the  mill — one  to  one,  or  less.  The  overflow 
from  this  can  be  carried  over  the  mill  into  the  discharge-box  to 
dilute  the  pulp  again  so  as  to  make  it  flow  through  launders. 

Platform. — There  should  be  a  platform  over  each  mill,  with  a 
hopper  over  each  man-hole  for  putting  in  pebbles,  and  the  pebbles 
should  be  brought  in  at  this  level  if  possible,  to  avoid  elevating 
them.  The  lifting  of  pebbles  into  the  side  of  the  mill  is  a  slow  and 
laborious  job.  This  platform  would  give  access  to  the  pulp-thick- 
ening cone  also.  With  everything  arranged  in  the  most  convenient 
manner,  the  mills  should  run  a  maximum  of,29J  days  per  month. 
If  there  are  only  a  few  pebbles  to  put  in,  two  or  three  men  will 
distribute  them  easily,  but  if  there  is  a  great  quantity  to  add, 
it  is  quicker  to  fill  the  mill  full  up  to  manhole,  put  on  the  door 
temporarily,  and  give  the  mill  a  few  turns  to  distribute  them, 
repeating  the  operation  until  sufficient  pebbles  have  been  intro- 
duced. At  El  Oro  they  keep  the  mills  one  to  three  inches  more 
than  half  full,  by  measurement  from  top  tube  to  pebbles.  When 
the  mill  is  opened  for  repairs  the  foreman  measures  the  pebbles 
and  can  tell  the  workmen  just  how  many  sacks  to  add.  They 
never  allow  them  to  wear  down  more  than  four  inches  before  re- 
filling. 

Liners. — The  Krupp  liners  at  El  Oro  are  1£  in.  thick,  of  chilled 
cast  iron;  the  chill  is  only  about  J  in.  deep,  and  when  it  wears  off, 
the  balance  of  the  plate  wears  much  faster.  The  wear  on  the  plates 
is  chiefly  at  the  head  of  the  tube,  and  diminishes  with  each  row 
of  plates  toward  the  tail.  The  average  life  of  Krupp 
plates  being  40  days,  with  mill  No.  3,  running  32  rev.  per  min., 
containing  7£  tons  of  pebbles  and  grinding  125  tons  of  sand  per  day, 
of  a  very  hard  quartz,  producing  about  50%  of  material  that  will 
pass  200-mesh,  40%  of  the  remainder  being  between  100  and  150 
mesh.  They  are  now  making  their  own  plates,  IJ-in.  thick,  of 


NOTES  ON  TUBE-MILLS  AT  EL  ORO,  MEXICO.        57 

white  cast  iron,  not  chilled,  but  it  is  run  in  very  thin  sand  molds. 
The  founder  has  a  formula  for  this  casting,  which  produces  a 
very  hard  metal  clear  through,  and  wears  evenly  and  equally 
down  to  a  quarter  inch  or  less.  It  was  not  possible  to  get  the  exact 
composition  of  the  iron,  but  any  intelligent  foundry-foreman 
could  soon  test  it  out,  as  a  hard  white  casting  is  made  by  using 
re-melted  iron  until  it  is  very  low  in  silicon,  and  adding  a  little 
sulphur.  No.  3  mill  has  four  rows  of  plates,  with  three  holes  each. 
The  length  is  to  be  changed,  making  three  plates  with  two  holes 
each  to  take  the  place  of  two  plates,  and  make  them  1^  in.  thick. 
At  El  Oro  they  never  empty  the  mill  to  re-line  it,  but  put  in  one 
or  more  plates  at  a  time  as  needed,  with  the  pebbles  all  in.  Thus 
the  IJ-in.  short  plate  will  be  lighter  to  handle  than  the  IJ-in. 
long  plate,  it  will  last  longer,  and  if  one  breaks  before  it  is  worn 
out  (as  they  sometimes  do),  there  will  be  less  iron  to  throw  away. 
These  plates  wear  much  longer  than  Krupp  plates,  and  cost  just 
half  as  much.  The  plates  must  be  cast  true  to  curve,  the  holes 
very  carefully  cored,  and  the  bolts  forged  from  common  iron  to 
exact  taper  of  hole.  When  the  plates  are  put  in,  see  that  the 
core  sand  is  thoroughly  cleaned  out  of  hole;  place  two  men  inside 
and  two  outside  of  mill ;  take  two  rods  2  ft.  6  in.  long  to  pass  through 
the  holes,  so  that  the  men  outside  can  help  to  lift  the  plate,  the 
rods  guiding  it  to  exact  position.  The  men  inside  can  easily 
hold  it  in  place,  while  the  rods  are  removed,  one  at  a  time,  and  the 
bolts  put  in.  Drive  the  bolts  to  a  firm  and  close  seat,  with  a 
sledge,  while  the  nut  is  being  tightened  with  a  2-ft.  wrench,  using 
a  washer  and  gasket  of  J-in.  sheet-packing  under  the  nut.  If  the 
plates  are  well  put  in  so  there  is  no  spring  and  the  bolts  fit  per- 
fectly, they  will  wear  evenly  down  to  ^  in.,  without  breaking  or 
causing  any  trouble.  Four  men,  after  they  become  familiar  with 
the  work,  will  take  out  old  plates  and  put  in  new  at  the  rate  of 
about  three  per  hour. 

At  El  Oro  they  have  found  that  the  end-discharge  plate 
or  grating  discharged  pebbles  too  large,  causing  undue  waste, 
and  have  thus  replaced  these  with  others  containing  oblong  holes 
|  in.  by  1J  in.,  there  being  48  holes  in  each  half  plate.  An  experi- 
mental run  has  been  made  with  mills  in  series,  that  is,  running  all 
the  coarse  sand  into  one  mill,  and  the  fine  return  sand  into  a  second 
mill.  The  consensus  of  opinion  is  that  this  is  the  best  and  most 
.economical  method  and  they  are  installing  two  new  mills,  to  be 


58  RECENT  CYANIDE  PRACTICE. 

put  in  series  with  the  old  ones.  The  pebbles  discharging  from  the 
first  mill  are  put  into  the  second,  where  a  fine  discharge  grate  is 
used,  the  pebbles  finally  issuing  being  not  more  than  f  to  J  in.  The 
discharge  must  be  into  an  open  box  containing  a  screen  with  about 
J-in.  holes  to  catch  the  pebbles.  They  have  in  use  a  No.  5  mill, 
5  ft.  diam.,  27  ft.  long,  inside  measure,  running  28  rev.  per  min., 
containing  16  to  17  tons  pebbles  and  8,640  kilo,  liners,  requiring 
107  h.p.;  a  No.  4  mill  5  ft.  by  24  ft.,  28  rev.  per  min.,  containing 
11  to  12  tons  pebbles,  7,520  kilo,  liners,  and  requiring  85  h.p.; 
and  a  No.  3  mill,  4  ft.  1  in.  by  19  ft.  9  in.  running  at  32  rev.  per 
min.,  containing  7£  tons  pebbles,  4,520  kilo,  liners,  requiring 
60  h.p.  They  have  determined,  after  several  months'  careful 
observation,  that  the  No.  3  mill  is  the  most  economical  and  effi- 
cient to  use,  and,  in  future,  they  will  install  no  other  size. 

The  consumption  of  pebbles  and  liners  for  the  months  of  Octo- 
ber and  November,  1905  (mills  running  95%  of  the  time)  was: 

Mill  No. 

3 

4 

5  . 


October 
Pebbles           Liners 
Kilo.               Kilo. 

November 
Pebbles            Liners 
Kilo.              Kilo. 

5,165 

1,365 

5,370 

1,360 

8,625 

729 

10,625 

2,589 

7,987 

1,345 

16,310 

2,589 

Total 21,777        3,439      32,305        6,538 

The  mills  were  grinding  about  8,700  tons  per  month  of  battery 
sand,  besides  the  return  sand. 

In  my  opinion  it  would  be  a  great  advantage  to  have  the  liner 
plates  short,  as  mentioned  above,  for  there  is  little  room  in  a  No.  3 
mill;  no  more  than  two  men  can  work  to  advantage,  and  the  plates 
should  be  light  enough  so  they  can  be  handled  quickly  and  easily. 
But  it  would  be  a  great  mistake  to  make  them  with  only  two  holes, 
because  if  a  bolt  cut  out,  the  leverage  of  the  plate  on  the  other 
bolt  will  soon  break  it,  causing  an  endless  amount  of  trouble, 
necessitating  a  shut-down  to  replace  a  bolt  at  once.  With  three 
bolts  in  a  plate,  if  one  comes  out,  the  other  two  will  hold  the  plate 
firmly  in  position  until  such  time  as  is  necessary  to  shut  down  for 
more  extensive  repairs. 


METALLURGICAL  DEVELOPMENT  ON 
THE  RAND 

BY  G.  A.  DENNY  AND  H.  S.  DENNY 

(June  2,  1906) 

As  far  back  as  July,  1903,  one  of  the  writers  had  the  temerity 
to  traverse  current  practice  and  make  many  alterative  suggestions 
representing  departures  of  a  radical  nature.  These  recommenda- 
tions were  substantially:  (1)  To  substitute  coarse  for  fine 
screen  on  batteries.  (2)  To  discard  all  mechanical  concentra- 
tion. (3)  To  separate  the  coarse  product  by  hydraulic  devices. 
(4)  To  re-grind  coarse  products  in  tube-mills.  (5)  To  provide 
secondary  amalgamation  tables  after  the  tubes.  (6)  To  improve 
the  methods  of  inter-handling  in  slime-plants.  (7)  To  make  use 
of  the  filter-press  in  the  treatment  of  slime.  (8)  To  investigate  the 
economical  possibilities  of  reducing  the  whole  of  the  mill-pulp  to 
a  fitness  suitable  for  filter-pressing,  and  thus  treat  one  product 
in  one  operation. 

The  point  upon  which  the  greatest  emphasis  was  laid  was  the 
necessity  for  fine  grinding,  and  overwhelming  evidence  was  pro- 
duced to  prove  conclusively  that  the  pyritic  constituent  of  the 
Witwatersrand  ore,  after  being  subjected  to  fine  grinding,  yielded 
its  gold  to  an  ordinary  cyanide  solution  as  readily  as  the  silicious 
portion  of  the  ore.  It  was  further  stated  that  by  the  use  of  the 
tube-mill  the  duty  of  the  stamps  would  be  increased  and  the 
extraction  improved. 

As  the  result  of  these  suggestions,  the  first  tube-mill  on  the 
Witwatersrand  was  introduced  at  the  New  Goch  mine,  and  this 
one  was  followed  a  little  later  by  several  others  at  other  mines. 
Since  that  time  there  has  been  a  good  deal  of  experience  gained 
in  the  use  of  the  tube-mill,  but  it  is  a  significant  fact  that  the 
recommendations  above  specified  in  regard  to  the  tube-mill, 
secondary  amalgamation,  coarse  screening  to  get  increased  stamp 
duty  and  higher  extraction,  have  been  followed  and  generally 
accepted  in  this  mining  centre.  The  further  suggestion  to  filter- 
press  has  not  been  followed  outside  of  the  group  of  mines  tech- 
nically controlled  by  the  writers,  and  many  other  departures  have 
since  been  jointly  advised  and  put  into  practice  at  the  Meyer  & 


60  RECENT  CYANIDE  PRACTICE. 

Charlton  and  the  New  Goch  mines.  It  is  on  the  results  of  the 
work  done  at  these  two  mines  that  the  writers  propose  to  base 
the  whole  of  the  statements  to  be  embodied  in  the  present  con- 
tribution. The  real  metallurgical  work  began  in  January,  1906, 
and  we  have  therefore  had  three  months  in  which  to  go  into  de- 
tailed investigation. 

The  consumption  of  water  at  the  Meyer  &  Charlton  is  now 
170  gal.  as  against  an  average  of  500  gal.  at  other  mines.  The 
actual  saving  is  illustrated  by  the  fact  that  whereas  before  the 
new  plant  was  installed  the  amount  of  water  available  was  only 
just  sufficient  to  meet  the  daily  requirements,  there  is  an  excess. 
today  of  over  100,000  gal.,  equal  to  some  300  gal.  per  ton  of  ore 
crushed.  The  consumption  in  the  metallurgical  plant  is  36.8  gaL 
per  ton  of  ore  crushed. 

At  the  Meyer  &  Charlton  plant  the  average  cost  of  cyanide  in 
March  was  4.19d.  per  ton  treated,  the  actual  consumption  of 
cyanide  being  half  a  pound,  equal  to  a  total  of  5,376  Ib.  The 
cost  of  lime  was  0.157d.  per  ton  treated,  the  actual  consumption 
being  0.8  Ib.  per  ton  treated,  the  total  consumption  being  8,460  Ib. 
The  total  amount  of  solution  in  circulation  amounted  to  2,133.3 
tons,  which  had  an  average  strength  of  0.038%  KCy,  and  an 
average  value  of  2  dwt.  gold  per  ton,  the  total  cyanide  contained 
being  1,638.05  Ib.,  and  the  total  gold  content  213  oz.,  the  alkalinity 
averaging  0.008  per  cent. 

The  average  amount  of  gold  dissolved  in  the  mortar  boxes 
is  1.37  dwt.  per  ton  of  ore  crushed.  The  effect  on  the  plates  is 
marked,  and  at  the  Meyer  &  Charlton  it  was  such  that  the  lower 
portion  of  the  plates  has  been  cut  off,  as  it  was  found  that  they 
were  doing  no  good  as  far  as  arresting  gold  was  concerned,  while 
on  the  other  hand  they  were  showing  signs  of  pitting  and  gradual 
disappearance  in  the  circulating  solution.  These  plates,  however, 
are  12  years  old,  and  were  thin  when  the  circulation  of  solution 
was  begun.  It  is  believed  that  an  electrolytic  action  is  set  up 
as  between  the  mortar-boxes  and  the  plates,  the  cyanide  solution 
being  the  medium;  hence  the  solution  of  the  copper.  A  number 
of  investigations  on  the  point  have  been  carefully  carried  out. 
It  is  estimated  that  the  life  of  copper  plates  with  circulating 
cyanide  solution  will  be  something  like  three  years,  and  it  may  be 
possible  by  the  short-circuiting  of  the  currents  set  up  between  the 
boxes  and  the  plates  to  reduce  the  solvent  action.  Assuming, 


ON  THE  RAND.  61 

however,  that  the  life  of  the  plates  is  only  two  years,  and  that 
the  plates  themselves  are  only  half  the  size  of  those  generally 
adopted,  the  cost  per  ton  becomes  insignificant. 

The  recovery  by  amalgamation  now  as  compared  with  the  old 
system,  illustrates  clearly  the  effect  of  taking  the  fine  gold  into 
solution,  the  respective  figures  being:  Recovery  by  amalgama- 
tion in  January,  1905,  50.124%;  recovery  by  amalgamation  in 
January,  1906,  45.202  per  cent. 

There  is  one  aspect  of  amalgamation  worthy  of  mention, 
and  that  is  the  danger  of  theft,  for  it  is  a  fact  that  there  is  a  big 
illicit  trade  in  amalgam,  and  the  writers  are  of  opinion  that  amalga- 
mation could  be  dispensed  with  altogeher  under  this  scheme.  The 
point  has  not  yet  been  proved,  but  it  can  easily  be  put  to  the  proof, 
and  this  will  be  done  in  the  near  future.  It  would  be  safer  to  have 
all  the  gold  in  one  place,  namely,  the  extractor  boxes. 

Originally  it  was  hoped  that  filter-pressing  would  be  unneces- 
sary. This  hope  was  based  on  the  assumption  that  a  product 
could  be  discharged  continuously  from  the  last  vat,  which  would 
contain  not  more  than  50%  moisture.  After  some  years  of  ex- 
perience the  conclusion  was  reached  that  this  was  impossible, 
and  at  the  Van  Ryn  mine,  two  years  ago,  an  arrangement  was 
built  for  returning  solution  from  the  slime-dam.  After  careful 
consideration,  however,  and  after  giving  due  weight  to  the  main- 
tenance of  slime-dams,  cost  of  pumping  back  solution,  losses  by 
absorption,  and  the  danger  of  the  dams  giving  way,  there  could 
be  no  further  doubt  that  filter-pressing  must  be  adopted  to  com- 
plete the  operation.  The  slime-plants  at  the  New  Goch  and  Meyer 
&  Charlton  are  now  simply  being  used  as  storage-tanks;  that  is 
to  say,  the  whole  of  the  available  gold  is  in  solution  before  the  slime 
reaches  the  slime-plant,  and,  therefore,  it  is  not  called  upon  to  do 
anything  in  that  direction.  At  the  Van  Ryn,  where  solution  is 
not  circulated,  the  slime-plant  is  showing  over  93%  of  the  total 
gold  in  solution  in  the  first  four  tanks.  At  the  Charlton,  however, 
with  the  circulating  solution,  this  gold  has  already  been  absorbed 
before  the  slime-plant  is  reached.  The  superiority  of  the  design 
of  this  plant  over  the  ordinary  type  of  decantation  plant,  is  that 
the  inter-handling  can  be  done  simply  by  the  regulation  of  a  valve 
and  at  no  cost;  and  as  a  storage  plant,  to  be  worked  jointly  with  a 
filter-press,  it  has  many  points  of  advantage. 

In  view  of  the  fact  that  the  circulating  solution  has  already 


62  RECENT  CYANIDE  PRACTICE. 

been  in  contact  with  the  sand  before  it  reaches  the  sand-plant, 
the  value  of  charges  under  present  conditions  shows  a  big  reduc- 
tion, and  from  an  8-dwt.  screen-assay  the  present  condition  gives 
a  return  in  the  settlers  of  under  1.5  dwt.,  and  in  the  treatment- 
tanks  of  1.4  dwt.,  which,  under  old  conditions,  would,  in  the  latter, 
have  been  in  the  neighborhood  of  5  dwt.  The  sand-plant  consists 
of  eight  vats  in  all,  four  of  which  are  superimposed  and  are  called 
the  'settlers,'  the  four  below  being  called  the  'treatment-tanks.' 
As  a  matter  of  fact,  however,  solution  is  being  pumped  to  the  set- 
tlers as  well  as  to  the  treatment  vats  almost  constantly,  and  by 
this  means,  instead  of  a  treatment  of  four  days,  which  would  have 
obtained  under  the  old  system,  a  treatment  of  nine  days  is  obtained. 
The  sand  plant  is  only  responsible  for  10%  of  the  total  gold  recov- 
ery, which  when  set  against  the  cost  of  operating  the  plant  and  the 
interest  on  capital  outlay,  at  once  proves  it  to  be  a  most  expensive 
department.  If  the  interest  on  capital  outlay  and  the  actual 
operating  costs  of  this  plant  be  allowed  as  a  credit  toward  the  cost 
of  all  sliming,  it  leaves  a  big  margin  in  favor  of  fine  grinding, 
and  the  intention  of  the  writers  on  this  evidence  is  entirely  to  dis- 
card the  department  so  generally  devoted  tqday  for  the  treatment 
of  sand.  Not  only  this,  but  the  residue  from  the  sand-plant  has 
neither  the  consistence  nor  the  low  value  of  the  filter-press  product, 
and  sufficient  investigation  has  been  done  to  indicate  that  if  coarse 
sand  be  reduced  to  150-mesh  it  can  be  filter-pressed  just  as 
well  as  ordinary  slime.  The  average  residue  then,  instead  of  being 
in  the  neighborhood  of  12  gr.,  would  be  reduced  to,  at  most,  six 
grains  per  ton. 

On  a  basis  of  96  tons  per  day  passing  through  the  tube-mill 
the  extra  revenue  is  £15  15s.  7d.  per  day  for  each  mill  in  use.  The 
deduction  generally  is  that  fine-grinding  is  a  necessary  corollary 
to  any  metallurgical  treatment  of  Rand  ore,  and  the  evidence 
points  to  the  further  extension  of  this  principle. 

Experimental  data  show  that  filter-pressing  is  one  of  the  most 
necessary  operations  that  has  yet  been  introduced  into  local 
practice.  The  points  are  the  great  saving  of  water,  the  increased 
extraction,  the  saving  of  cyanide,  the  economy  of  time  in  treat- 
ment of  slime,  and  the  production  of  a  better  product  for  handling 
on  the  slime-dump.  The  operation  is  one  of  the  very  simplest, 
and  experienced  white  men  who  have  been  filter-pressing  for  many 
years  in  Western  Australia  are  quite  satisfied  that  the  native  is  just 


ON  THE  RAND.  63 

as  good  a  filter-pressing  hand  as  the  white  man.  The  reason  why  this 
method  was  not  adopted  earlier  was  due  to  the  fear  of  excessive 
cost.  Our  figures  not  only  disprove  this  idea,  but  show  that  filter- 
pressing  is  the  most  important  operation  in  the  whole  range  of 
treatment.  The  average  residue  from  slime  during  March  at  the 
Charlton  contains  0.2886  dwt.  The  fineness  of  the  gold  was  753.- 
962,  and  the  amount  of  acid  used  4,988  lb.,  equal  to  1.304d.  per 
ton  treated;  and  the  amount  of  zinc  used  3,834  lb.,  valued  at  £63 
18s. 

The  addition  of  a  filter-press  plant  to  the  mill  settles  one  point 
that  is  usually  subject  to  inaccuracy,  and  that  is  the  tonnage  of 
slime  handled.  The  relation  of  extraction  to  tons  multiplied 
by  screen-assays  has  not,  in  the  past,  been  so  close  that  this  point 
has  come  up  for  serious  discussion,  but  in  the  future  there  is  no 
doubt  that  more  attention  will  have  to  be  given  to  it : 

The  costs  for  the  month  of  March  are  as  follows : 


Cost  per  ton 

Cost  per  ton 

Total  cost 

milled. 

treated 

Pounds. 

Pence. 

Pence. 

Tailing-elevator     

279 

6.23 

6.23 

Sand-treatment  

447 

9.99 

14.08 

Slime-treatment 

362 

8.08 

27.82 

Extractor-house  

436 

9.73 

9.73 

Total  cost 1 ,524  34.03  57.86 

It  will  be  noticed  from  this  statement  that  the  cost  of  elevating 
the  pulp  is  high,  figuring  at  6.232d.  per  ton  milled.  Apart  from 
this  cost,  the  actual  expenditure  is  27. 81  Id.  per  ton  milled.  When 
it  is  considered  that  this  covers  the  whole  cost  of  sand-treatment 
and  slime-treatment,  including  filter-pressing  and  the  cost  of  dump- 
ing residue,  this  result  must  be  regarded  as  eminently  satisfactory 
for  a  new  plant. 

As  already  indicated,  the  sand-plant  is  only  responsible  for 
10%  of  the  gold  recovered;  while  the  slime-plant  is  doing  nothing, 
and  therefore  is  not  required.  The  highest  residue  is  in  the  sand- 
plant,  and  the  costs  of  running  it  are  also  high.  The  final  conclu- 
sions on  actual  data  are  (1)  that  the  credit  of  the  cost  of  re-grinding 
to  be  established  by  discarding  the  sand-plant,  and,  allowing  for 
the  interest  on  the  capital  outlay  and  the  actual  working  costs  of 
the  sand-plant,  is  more  than  is  required  to  cover  the  whole  of  the 


64  RECENT  CYANIDE  PRACTICE. 

cost  of  re-grinding;  (2)  that  the  extraction  on  the  one-product 
basis,  where  everything  would  be  filter-pressed,  shows  a  further 
improvement  in  favor  of  all-sliming;  (3)  that  a  plant  on  the  all- 
s'.iming  basis  could  be  erected  complete  at  somewhat  less  than 
50%  the  cost  of  the  ordinary  sand  and  decantation  slime-plants 
of  today,  to  give  a  much  higher  and  far  more  consistent  recovery, 
and  to  be  worked  at  a  much  lower  cost.  In  the  design  of  the  all- 
sliming  plant  the  stamp  battery  is  left  out,  the  principle  being  crush- 
ing and  grinding  in  stages. 

The  grinding  analyses  of  the  products  show  some  curious  fea- 
tures. One  in  particular  is  that  the  grading  of  a  settled  sand  is  quite 
different  from  the  grading  of  the  charge  which  that  sand  represents 
when  transferred  from  the  top  to  the  bottom  tank.  It  is  diffi- 
cult to  determine  exactly  how  this  change  is  brought  about;  but, 
as  the  results  have  been  confirmed  in  many  investigations,  there 
can  be  no  question  that  the  change  does  take  place.  It  may  be 
said  that  work  could  not  be  carried  out  satisfactorily  without  grad- 
ing analyses. 

Shortly  after  starting  the  plants,  the  residue  value,  both  in 
the  slime  and  the  sand  plants,  occasionally  was  high.  In  every 
case,  it  was  found  that  high  residues  were  due  to  reasonable 
causes,  such  as  could  easily  be  controlled  when  the  operators 
had  a  full  knowledge  of  the  conditions.  There  is  no  reason  why 
the  filter-press  residue  should  ever  be  higher  than  6  gr.  or  the  sand- 
residue  be  higher — given  that  the  tube-mills  are  running — than  12 
gr.,  and  this  quite  apart  from  the  screen-assay.  Taking  the  case 
of  the  Meyer  &  Charlton,  however,  which  in  March  had  an  aver- 
age screen-assay  of  10.871  dwt.,  the  average  residue  in  the  sand 
was  144  gr.,  and  in  the  slime  6.91  gr.  The  percentage  of  the  total 
pulp  represented  by  sand  was  70.763,  and  the  slime  29.050.  This 
gives  an  average  residue  of  12.39  gr.,  equal  to  an  extraction  on  the 
screen  assay  of  95.302%.  The  total  gold  cleaned  up  shows  an 
actual  extraction  of  95.5%.  In  this  plant  96%  theoretical  extrac- 
tion should  be  easily  and  consistently  realized,  and  allowing  for  1% 
loss  in  the  smelt  and  clean-up,  etc.,  the  actual  gold  in  the  bank 
should  be  95  per  cent. 


THE  TREATMENT  OF  DESERT  ORES 

(June  23,  1906) 

The  Editor: 

Sir — I  have  read  Mr.  Bosqui's  article  in  your  issue  of  May  26, 
in  reply  to  one  of  mine  in  your  issue  of  Arpil  28,  and  crave  space 
to  rectify  a  few  points. 

The  term  'desert  ore'  was  not  used  by  me  as  a  term  of  classi- 
fication of  ore;  it  meant  simply  ore  found  in  desert  regions,  and 
referred  particularly  to  the  conditions  of  treatment  there.  I  did 
not  refer  specially  to  Mr.  Bosqui's  installation  of  the  Combination 
mill  or  to  the  ore  of  any  particular  district,  but  referred  generally 
to  the  treatment  of  soft  oxidized  ores.  Mr.  Bosqui's  description 
of  the.  Combination  ore,  as  one  in  which  the  oxidized  portion  is 
much  harder  than  the  sulphide  ore,  shows  it  to  be  an  unusual 
occurrence. 

"The  latest  and  best  practice  in  cyaniding,"  quoted  by  Mr. 
Bosqui,  would  be  more  correctly  termed  the  "last  fashion  in 
cyaniding  in  South  Africa."  It  is  notorious  that  what  was  called 
"double  treatment"  was  boomed  some  years  ago  in  South  Africa, 
and  in  consequence  a  number  of  double-treatment  plants  were  in- 
stalled in  this  and  other  countries;  and  they  were  failures.  More 
recently,  the  South  African  practice  was  to  divide  the  pulp  into 
'sand'  and  'slime'  to  be  separately  treated,  and  this  appears  to  be 
the  ideal  treatment  for  "every  modern  mill  operating  on  a  logical 
basis,"  according  to  Mr.  Bosqui.  The  most  recent  practice, 
however,  at  Johannesburg,  is  to  fine-grind  and  filter-press  the  whole 
pulp,  and  thus  get  "one  product  in  one  operation,"  the  advantages 
of  which  are  most  clearly  and  interestingly  shown  in  the  abstract 
of  Messrs.  Denny's  article  given  in  your  issue  of  June  2. 

I  shall  not  take  up  space  by  replying  to  Mr.  Bosqui's  state- 
ments on  ore  treatment  seriatim,  but  I  must  traverse  one  state- 
ment regarding  "the  impossibility  (from  an  economic  standpoint) 
of  reducing  ore  to  a  sufficient  fineness  to  ensure  the  best  recovery" 
by  referring  to  the  fine-grinding  of  cement-clinker,  which  is  done  on 
an  enormous  scale  and  at  a  low  cost. 

It  appears  to  me  that  the  "best  practice"  is  to  be  able  to  inter- 
pret laboratory  results  on  any  ore,  so  as  to  install  the  kind  of  plant 


66  RECENT  CYANIDE  PRACTICE. 

economically  best  suited  to  its  treatment,  without  reference  to 
what  may  be  the  practice  in  South  African  or  other  fields,  otherwise 
than  to  take  advantage  of  new  discoveries  in  grinding  machines, 
etc.  In  the  case  of  porous  oxidized  surface  ore  it  appears  to  me 
that  the  best  practice  would  be  to  crush  dry  to  a  fairly  coarse  mesh 
and  leach  direct  in  vats,  the  residue  being  subsequently  passed 
over  amalgamating  plates  or  concentrators,  if  found  to  pay.  In 
the  case  of  ore  which  requires  fine-grinding  to  release  the  metals, 
I  would  fine-grind  either  dry  or  with  cyanide  solution,  agitate,  and 
filter-press  the  whole  pulp,  thus  getting  "one  production  in  one 
operation."  The  point  on  which  I  wish  to  lay  most  stress  was 
that  when  cyanide  is  used  at  all,  it  is  more  logical  to  treat  with 
cyanide  first  and  amalgamate  (when  necessary)  afterward,  than 
to  follow  the  ordinary  procedure. 

Finally,  I  wish  to  deprecate  most  strongly  the  introduction 
of  the  personal  element,  as  so  patently  shown  by  Mr.  Bosqui. 
I  take  it,  these  discussions  should  be  purely  impersonal  and  for 
the  advancement  of  the  art  of  metallurgy  and  the  interest  and  in- 
struction of  your  readers,  but  not  for  the  ventilation  of  any  per- 
sonal feeling  between  professional  men. 

BERTRAM  HUNT. 

San  Francisco,  June  9,  1906. 


PROGRESS  OF  CYANIDATION 

(Editorial,  July  28,  1906) 

The  comment  on  current  practice  at  Kalgoorlie  by  Mr.  Alfred 
James,  will  interest  cyaniders.  We  also  publish  a  description  of 
a  new  method  of  lining  tube-mills,  as  devised  by  Mr.  H.  P.  Barry, 
of  the  great  Waihi  mine,  in  New  Zealand.  One  of  the  practical 
problems,  especially  to  millmen  operating  at  a  distance  from 
manufacturing  centres,  is  the  cheapest  and  most  durable  lining 
for  the  tubes.  At  first  everyone  depended  upon  Iceland  pebbles 
and  silex  lining  from  Europe;  and  to  those  in  charge  of  mills  on 
the  other  side  of  the  world — in  Australia,  New  Zealand,  and  Mexico, 
for  example — it  was  a  serious  handicap  to  depend  on  supplies 
from  so  great  a  distance.  Iron  linings  of  special  composition 
were  not  much  better,  for  they  also  were  made  by  methods  not 
available  at  the  ordinary  mining  town.  Both  in  Mexico  and  New 
Zealand  the  mill-managers  have  succeeded  in  breaking  away 
from  the  tyranny  of  a  special  material  and  they  have  been  able 
also  to  procure  flints  suitable  for  their  purpose.  The  device  in- 
vented by  Mr.  Barry  is  one  of  the  best  improvements  in  tube-mill 
practice,  and,  as  it  is  applicable  to  other  localities,  we  hope  it  may 
prove  extremely  useful. 

In  regard  .to  cyanidation  generally,  Mr.  James'  remarks  are 
much  to  the  point.  The  frequent  comparisons  between  the  work 
done  by  the  pans  and  tube-mills  at  Kalgoorlie  have  evidently 
been  of  little  value  as  indicating  the  general  applicability  of  the 
two  machines,  simply  because  the  peculiar  conditions  obtaining 
at  Kalgoorlie  have  been  overlooked.  Mr.  James  sets  that  matter 
right.  His  other  criticisms  are  welcome,  and  any  reply  to  them 
will  be  given  a  courteous  hearing. 

It  appears  likely  that  tube-mills  will  be  discarded  at  Kalgoorlie 
because  the  tellurides  occurring  in  the  ore  require  roasting;  the  idea 
used  to  be  to  comminute  excessively  so  as  to  dissolve  these  tellurides 
raw,  but  now  solubility  is  secured  by  obtaining  the  porous  condi- 
tion due  to  a  roast.  Filter-presses  are  already  a  back  number  in 
Western  Australia,  and  elsewhere.  Filter  machines  of  the  Moore, 
Butters,  and  other  types  are  displacing  the  old  devices.  In  fact, 
cyanide  practice  is  undergoing  a  continual  and  rapid  develop- 


68  RECENT  CYANIDE  PRACTICE. 

ment,  one  device  after  another  being  elbowed  out  of  the  way  to 
make  room  for  something  better.  Just  now  it  is  manifest  that 
it  is  cheaper  to  treat  slime  by  agitation  than  to  treat  sand  by 
percolation;  it  is  not  only  a  question  of  relative  cost  between 
re-grinding  plus  slime-treatment  on  the  one  hand  and  percolation 
of  the  coarse  stuff  on  the  other;  the  assertive  factor  is  the  increase 
of  crushing  capacity  in  the  first  instance — whether  under  stamps 
or  between  rolls — due  to  relieving  the  first  crusher  of  the  work 
of  pulverizing.  On  these  subjects  we  hope  to  hear  from  our  friends. 
Experiments  are  continually  under  way;  the  exchange  of  experience 
will  prove  mutually  helpful. 


TUBE-MILL  LINING 

(July  28,  1906) 

Those  who  operate  tube-mills  will  not  need  to  be  told  of  the 
want  of  a  cheap  and  durable  form  of  lining,  for  this  is  one  of  the 
practical  problems  in  this  branch  of  milling.  At  the  Waihi  mine 
in  New  Zealand,  the  tube-mill  has  proved  most  effective  for  re- 
grinding  and  the  practice  has  been  developed  under  the  direction 
of  Mr.  H.  P.  Barry,  the  superintendent  of  works.  Formerly  at 
Waihi  they  crushed  under  stamps  to  40-mesh,  and  the  finer  the 
pulp  discharged  from  the  battery,  the  better  the  extraction  in 
the  cyanide  annex;  but  there  was  a  limit  to  fine  crushing,  for  be- 
yond 40-mesh  the  duty  of  the  stamps  was  decreased  until  excessive 
pulverization  was  no  longer  economical.  Now  the  stamps  crush 
only  to  15  or  20-mesh  and  the  battery  product  is  re-ground  in 
tube-mills  to  150-mesh.  There  was  lots  of  trouble  and  expense 
in  connection  with  the  lining  of  the  tubes  for  the  distance  of 
New  Zealand  from  Europe  represents  a  maximum  length  of 
transport.  The  silex  from  Iceland  had  to  be  laid  with  a  special 
cement  and  the  fitting  of  the  pieces  was  troublesome.  It  cost 
£80  to  line  one  tube-mill,  and  the  time  of  service  was  only  three 
months.  Now  Mr.  Barry  employs  an  invention  (patented)  of 
his  own,  whereby  he  utilizes  the  flinty  portions  of  the  Waihi  ore 
and  lays  them  in  portland  cement;  the  lining  lasts  six  months 
and  costs  £40  —  the  service  is  twice  as  long  at  one-half  the  ex- 
pense, it  is  four  times  cheaper. 

This  lining  is  illustrated  herewith,  by  courtesy  of  Mr.  Charles 
Rhodes,  general  manager  of  the  Waihi  Gold  Mining  Co.,  Ltd.  It 
is  called  Barry's  honeycomb  liner  and  it  is  formed  of  cast-iron 
segments,  curved  to  the  shape  of  the  tube,  in  sections  having 
four  or  six  divisions,  each  four  by  six  inches.  In  actual  operation 
it  has  been  found  that  the  costs  are: 


Honeycombed  casting,  28  cwt.  @  15s 

Broken  quartz,  5  tons  @  20s  ............................ 

Portland  cement,  1  ton  at  mine  @  11s.  per  cask  ............       4 

Sand  (rough  tailing)  ,  1  ton  ..............................       1 

Labor  @  9s.  per  day   ...........  ........................      8 


70 


RECENT  CYANIDE  PRACTICE. 


We  are  informed  that  the  Waihi  company  is  making  the  cast- 
ing in  its  own  foundry  for  12s.  per  cwt.  and  that  the  cost  put  down 
for  broken  quartz  is  rather  excessive,  so  that  the  liner  can  be  made 
for  £30.  The  saving  is  about  £260  per  tube  per  annum,  as 
compared  to  the  old  method.  As  the  Waihi  company  is  about  to 
use  10  or  12  tube-mills,  the  saving  will  be  important,  about  $15,000 
per  year. 

We  quote  herewith  from  the  specification  of  Mr.  Barry's 
patent,  and  accompany  it  with  two  of  the  diagrams  that  accompany 
that  claim  for  patent : 

The  purpose  of  this  invention  is  to  provide  a  cheap  and  effec- 
tive grinding  surface  within  tube-mills  and  other  grinding-machines. 


Fig.  1.     Tube-Mill  Lining.     Plan. 

This  purpose  is  attained  by  fitting  within  the  tube-mills  shallow 
frames  or  boxes  of  hexagonal  or  rectangular  form  shaped  as  is 
hereafter  stated,  or  in  any  other  shape  which  will  conveniently 
fit,  and  in  fixing  therein  a  material  composed  of  rough  blocks 
of  stone  or  other  substances  suitable  for  the  purpose.  The  accom- 
panying drawing  shows  16  figures  of  which  Fig.  1  is  a  plan  illus- 
trating a  portion  of  the  inside  of  a  tube-mill  and  showing  different 
formations  of  frames  or  segments  with  material  fixed  in  parts, 
while  Fig.  2  is  a  cross-section  through  X-X  of  Fig.  1 . 

The  tube-shell  A  of  the  grinding-mill  is  shown  in  Fig.  1  and  2 
in  part  and  broken,  as  it  is  only  necessary  to  show  a  portion  to 


TUBE-MILL  LINING.  71 

illustrate  the  different  formations  or  segments  B  fixed  and  which 
may  be  fixed  therein.  Fig.  2  being  a  cross-section  only,  the  depths 
of  the  formations  or  segments  B  are  shown,  but  Fig.  1  being  a 
plan,  their  shapes  are  shown  more  fully  so  that  the  idea  of  their 
purpose  can  be  fully  seen  while  the  rough  stones  C  shown  in  both 
figures  quite  illustrate  the  advantage  of  their  use. 

The  frame  and  box  formations  5,  hereinafter  called  segments, 
are  made  with  or  without  bottoms  of  iron,  steel,  or  other  suitable 
material  and  in  convenient  sizes  shaped  to  fit  inside  the  tube-mill, 
as  shown  in  Fig.  1  and  2,  and  to  retain  the  lining  material  in  posi- 
tion. The  segments  B  may  have  ribs  or  bars  D  preferably 
shaped  across  to  help  hold  the  lining  material  C  in  place  and  so  as 
to  limit  and  reduce  the  size  of  the  segments  B  into  smaller  com- 
partments E  to  suit  the  particular  nature  of  the  lining  material 
used,  or  rib  or  bar  formations  D  may  be  used  by  themselves  with- 
out outer  frames. 


Fig.% 

Fig.  2.     Tube-MiL  Lining.     Section. 

The  outsides  F  of  the  segments  B  may  be  formed  plain  and 
made  to  the  radius  of  the  tube-mill  and  so  form  an  arch  which  will 
key  each  segment  B  in  position,  or  the  outsides  of  the  segments 
B  may  be  rabbet-formed  so  as  to  interlock  with  grooves  therein 
into  which  locking  bars  of  iron  or  steel  or  other  suitable  material 
may  be  put.  The  segments  J5  may  be  bolted  or  otherwise  suitably 
connected  to  the  tube-mill,  but  as  a  rule  this  will  be  unnecessary. 

To  prepare  the  segments  B  for  use  they  are  placed  upon  a 
firm  surface  approximately  of  the  same  radius  as  the  inside  of  the 
tube-mill  when  they,  the  segments  B,  are  well  filled  with  the  lining 
material  either  in  the  form  of  concrete  K  or  of  rough  blocks  of 
stones  C,  the  stones  being  jammed  in  tightly  and  the  interstices 
between  them  being  filled  and  rammed  with  cement,  concrete 
or  cement  mortar  M  or  suitable  material  which  can  be  poured 


72  RECENT  CYANIDE  PRACTICE. 

in,  in  the  shape  of  grouting,  if  the  spaces  between  the  stones 
are  small.  The  lining  material  may  be  fixed  to  be  quite  rough 
as  shown  at  C  in  Fig.  2  and  it  will  preferably  be  made  to  project 
in  irregular  formations  above  the  edges  of  the  segment  B  and  ribs 
or  bars  D,  as  it  will  thereby  protect  the  edges  from  undue  wear, 
and  by  its  irregular  surface  assist  the  grinding  capacity  of  the  tube- 
mill  or  machine.  The  lining  material  may  be  of  quartz  or  any 
hard  rock  or  material  that  will  do  the  work  required  of  it. 

After  giving  the  cement  concrete  or  the  cement  mortar  M 
or  concrete  K  or  other  lining  material  in  the  segments  B  ample 
time  to  set  hard,  the  segments  B  are  built  into  the  tube-mill  or 
machine  with  cement  or  other  suitable  binding  material  and  the 
locking-bars  are  driven  in  when  found  necessary  to  use  them.  If 
found  advantageous  to  do  so,  the  segments  B  may  be  built  into 
the  tube-mill  or  machine  empty  in  the  first,  place  and  then  the 
different  compartments  can  be  filled  with  the  lining  material 
in  the  manner  above  described.  When  the  different  segments 
B  have  been  fitted  within  the  tube-mill  or  machine  and  the 
lining  material  filled  and  fixed  therein,  the  tube-mill  or  machine 
will  be  worked  in  the  usual  way  but  with  a  much  more  effective 
and  marked  result  than  is  now  obtained  without  the  use  of  the 
lining  material  herein  specified.  After  the  tube-mill  or  machine 
has  been  working  for  some  time,  the  lining  material  should  be 
examined,  and  if  any  of  it  is  found  to  be  faulty  or  unfit  for  use, 
the  segment  B  into  which  it  is  fitted  or  fixed  can  be  re-fitted  by 
having  the  faulty  lining  chipped,  broken,  and  taken  out  and  fresh 
lining  material  filled  in,  in  the  manner  already  described. 


CRUSHING  AND  GRINDING  PRACTICE  AT 
KALGOORLIE 

BY  ALFRED  JAMES 

(July  28,  1906) 

At  a  moment  when  one  hears  so  much  as  to  the  relative  ad- 
vantages of  stamps  and  the  ball-mills,  tube-mills,  and  pans,  one  is 
apt  to  overlook  the  particular  practice  which  has  led  to  the  intro- 
duction of  a  special  type  of  machine  to  effect  a  certain  definite 
reduction  on  a  definite  class  of  ore.  Thus,  for  example,  pans  were 
introduced  at  Kalgoorlie  to  collect  coarse  gold  from  the  furnace 
product,  to  get  rid  of  soluble  salts  before  cyaniding,  and  to  grind 
coarse  on  sintered  particles  of  ore.  For  this  purpose  pans  have 
proved  remarkably  successful  and  if  the  all-roasting  process  had 
continued  unchallenged,  probably  they  would  have  maintained 
their  superiority  unquestioned. 

But  the  advent  of  Dr.  Diehl  and  bromo-cyanide  changed  all 
that,  or  rather,  for  a  time,  threatened  to  do  so.  Dr.  Diehl  claimed 
to  be  able  to  do  away  with  roasting  entirely,  and  to  attain  this  ob- 
ject a  new  type  of  ore-reducing  machine— a  fine  slimer — was  neces- 
sary, and  he  introduced  the  tube-mill  for  this  purpose. 

It  is  necessary  at  the  outset  to  bear  this  distinction  in  mind, 
for  if  the  all-roasting  process  becomes  once  more  universal  or  if 
it  is  possible  by  closer  or  improved  concentration  to  reduce  the 
refractory  material  (that  is  the  sulpho-tellurides)  in  the  pulp  to 
an  inappreciable  or  immaterial  amount,  then  it  may  be  reasonably 
expected  that,  with  the  absence  of  the  necessity  for  fine-sliming, 
pans  will  prove  advantageous  rather  than  tube-mills  on  account  of 
their  lower  horsepower  per  unit,  their  greater  convenience  in  work- 
ing, their  capacity  for  amalgamation,  and  the  granular  nature  of 
their  product.  These  remarks  refer  to  the  Kalgoorlie  practice  only 
and  not  to  districts  where,  for  example,  the  finest  comminution 
possible  per  horsepower  unit  is  necessary  for  effective  amalgama- 
tion or  for  a  high  extraction  generally. 

Therefore,  similarly,  given  an  ore  which  yields  the  most  profit- 
able result  by  roasting,  we  can  scarcely  expect  stamps  to  be  pre- 
ferred for  crushing  purposes,  because  the  question,  for  example,  of 
drying  the  ore  is  of  greater  moment  than  the  less  repairs  required 


74  RECENT  CYANIDE  PRACTICE. 

by  stamps  as  compared  with  ball-mills.  The  latter,  moreover, 
appear  to  have  the  further  advantage  of  requiring  less  power 
per  ton  crushed,  yielding  as  they  do  an  output  of  two  tons  of 
hard  ore  per  h.p.  day  through  30  to  40  mesh  or  2J  tons  per  h.p. 
day  through  a  25-mesh  screen — a  record  unapproached  by  stamps, 
which  require  re-grinding  appliances  absorbing  considerable 
power  when  large  outputs  (7  to  10  tons  per  stamp)  are  to  be  at- 
tained. The  best  practice  known  to  the  writer  in  this  direction 
with  the  ordinary  gravitation  stamp  is  336  tons  coarse  crushed 
by  40  stamps  (1,250  Ib.)  for  120  h.p.  plus  an  extra  60  h.p.  for  the 
tube-mill  necessary  to  crush  the  240  tons  coarse  product  to,  say, 
30  to  40-mesh,  or  under  two  tons  per  h.p.  day. 

It  thus  appears  that  stamps  will  be  preferred  only  when  the 
ore  yields  a  considerable  proportion  of  gold  on  the  plates  and  when 
roasting  is  not  to  be  adopted.  At  Broken  Hill,  where  there  is 
no  amalgamation,  the  crushing  being  preparatory  to  wet  concen- 
tration, they  even  prefer  to  wet-crush  in  ball-mills  rather  than 
stamps,  but  sufficient  data  are  not  yet  available  to  establish 
the  economy  of  this  practice. 

As  to  the  relative  efficiency  of  the  ball  and  Griffin  mills,  apart 
from  the  questions  of  cost,  power,  and  repairs,  the  regular  granular 
product  of  the  ball-mills  appears  so  much  superior  for  roasting 
purposes  to  the  cement  (fine  plus  coarse)  granules  of  the  Griffin 
mills,  that  it  looks  as  if  the  latter  would  not  continue  in  favor, 
though  one  can  quite  understand  their  installation  years  ago 
when  dry-crushing  results  were  less  established. 

And  now  as  to  pans  versus  tube-mills :  If  better  concentra- 
tion can  show  a  reasonably  free  cyaniding  product,  then  the  neces- 
sity at  Kalgoorlie  for  tube-mills  disappears  with  the  theory  of  a 
complete  non-roasting  treatment,  which,  as  stated  above,  was  the 
primary  cause  of  their  adoption.  But  it  is  by  no  means  yet  decided 
—rather  the  reverse — that  concentration,  as  practised  in  this  dis- 
trict, is  yielding  a  product  capable  of  being  bromo-cyanided  with- 
out the  very  finest  sliming,  such  as  it  appears  tube-mills  only  can 
as  yet  accomplish.  It  must  be  remembered  that  even  the  finest 
sliming  gives  only  comparatively  fair  results  on  the  material 
that  is  bromo-cyanided.  It  was  the  amalgamation  recoveries 
from  the  Old  Lake  View  and  Hannan's  Star  plants  which  brought 
the  percentage  recoveries  to  so  high  a  figure,  and  an  attempt 
to  obtain  Dr.  Diehl's  bromo-cyanide  extractions  by  bromo-cya- 


CRUSHING  AND  GRINDING  PRACTICE.  75 

nide  alone  without  Dr.  Diehl's  bromo-cyanide  method — tube-mill 
fine-sliming — is  apt  to  yield  as  poor  results  as  are  shown  by 
one  of  the  best  known  mines  at  Kalgoorlie.  Even  though  the 
ore  of  this  mine  is  supposed  to  be  comparatively  free  from  refrac- 
tory minerals,  the  residues  are  reputed  to  be  the  highest  in  the 
locality — 2J  dwt.  per  ton. 

Surely,  in  comparing  the  relative  efficiencies  of  pans  and 
tube-mills,  an  extraction  test  would  have  been  more  useful,  more 
accurate  and  more  practical  than  the  pan  versus  tube-mill  test 
published  by  the  Ivanhoe  Company.  Of  what  value  is  a  150-mesh 
minimum  when  dealing  with  the  classification  of  tube-mill  products? 

But  with  regard  to  these  tests,  they  were  not  referred  to  more 
definitely  in  my  remarks  published  in  The  Engineering  and  Mining 
Journal,  because  it  was  evident  from  the  immatureness  of  the 
methods  that  the  results  of  the  tests  were  unworthy  of  serious 
consideration.  One's  chief  regret  was  that  names  of  such  high 
standing  should  have  been  tacked  onto  tests  so  badly  carried  out. 
To  those  conversant  with  tube-mill  work,  it^is  unnecessary  to  insist 
on  the  absolute  need  of  keeping  the  feed-pulp  free  from  slime 
and  for  taking  the  finished  product  away  from  the  mill  immediately 
it  is  formed;  but  the  Ivanhoe  not  only  included  a  huge  proportion 
of  slime  in  its  feed— returning  the  finished  product  to  the  mill 
instead  of  taking  it  away  at  once — but,  by  the  intermediate 
working  of  the  test  on  alternate  days,  actually  had  the  flints 
coated  with  slime  at  the  start  of  each  daily  test. 

We  have  the  extraordinary  position  of  a  man  who  discovers 
that  an  original  feed  or  more  than  26  tons  per  day  chokes  his  tube- 
mill,  actually  feeding  no  less  than  26.77  tons  of  finished  slime 
(finer  than  150-mesh),  or  more  than  he  takes  out  (25.15  tons) 
for  his  daily  output.  Could  any  one  expect  a  mill  thus  choked 
.to  do  effective  work?  Can  anyone  longer  wonder  why  the  results 
show  only  a  fraction  of  the  work  done  per  h.p.  unit  consumed, 
compared  with  that  done  elsewhere  by  the  same  h.p.  unit?  And 
so  it  happens  that  we  have  seen  published  all  over  the  earth,  results 
which  must  be  due  to  the  enthusiasm  of  inexperience,  rather  than  to 
any  attempt  or  desire  to  deliberately  mislead. 

The  actual  daily  production  of  the  tube-mill  choked  with 
fine  slime  was  only  16.74  tons  of  '-  150'  slime,  although  the  daily 
output — including  the  returned  slime  re-ground — was  no  less  than 
43.46  tons.  Could  anything  be  more  misleading  than  figures 


76  RECENT  CYANIDE  PRACTICE. 

made  out  on  such  a  basis?  One  is  tempted  to  wonder  why  the 
metallurgist  responsible  did  not  go  a  little  further  and  reduce 
the  position  ad  absurdum,  by  returning  all  his  finished  product, 
thus  proving  that  the  tube-mill  was  doing  no  work  at  all ! 

The  tests  were  thus  unworthy  of  serious  notice  mainly  because 
the  lack  of  opportunity  for  the  free  escape  or  removal  of  the  finished 
tube-mill  product  reduced  them  to  an  absurdity.  On  the  other 
hand  the  pans — especially  the  first  pan — were  allowed  a  much  better 
opportunity  of  getting  rid  of  their  finished  product,  though  even 
here  the  arrangements  might  have  been  improved.  The  first  pan 
received  only  7J  tons  of  slime  with  an  original  feed  of  21.3  tons  of 
sand,  as  against  the  tube-mill  quota  of  26.77  tons  of  slime  with  an 
original  feed  of  19.5  tons  of  sand  only.  Had  some  more  efficient 
comparison  of  the  product  than  the  150-mesh  screen  been  available, 
the  effect  of  the  continuous  re-grinding  of  the  tube-mill  finished 
product  must  surely  have  been  apparent. 

In  the  above  remarks  reference  is  made  to  the  slime  grinding 
tests  only.  I  have  already  shown  elsewhere  that  given  the  ordi- 
nary costs  of  flints  and  liners  in  place  of  the  extraordinary  costs 
stated,  the  advantage  lay  with  the  tube-mill  even  apart  from  the 
considerations  of  limitation  of  output  referred  to  above ;  and  this 
remark  refers  also  to  the  fine  grinding  (breaking  down  coarse  sand) 
experiments.  Setting  flints  and  liners  down  at  1.75d.  to  2d.— 
which  is  the  ordinary  cost — the  relative  costs  per  ton  ground  are 
8.86d.  for  tube-mills,  as  against  10.32d.  with  pans. 

In  this  connection  it  is  curious  that  in  Western  Australia 
they  should  still  use  cast-iron  linings,  which  appear  to  have 
become  obsolete  in  other  places.  In  the  recent  discussion  at  Johan- 
nesburg Mr.  Leupold,  general  manager  of  the  Treasury  mill  (using 
the  Krupp  tube)  stated  that  he  entirely  concurred  with  Mr. 
Bowling  as  to  the  superiority  of  flint  liners,  "which  roughly  cost 
one-half  and  last  twice  as  long  as  the  chilled  iron  ones." 

Pans  have  proved  themselves  reliable,  efficient,  and  conve- 
nient where  roasting  is  employed,  but  there  appears  as  yet  no 
proof  of  such  efficiency  on  unroasted  sulpho-telluride  tailing; 
on  the  contrary,  the  evidence  to  date  seems  all  in  favor  of  the  use 
of  the  tube-mill  on  such  material. 

By  the  way,  one  cannot  but  be  surprised  at  the  difference  of 
opinion  obtaining  locally  as  to  the  working  of  pans.  No  two  neigh- 
boring metallurgists  seemed  to  be  of  the  same  opinion.  Thus  at 


CRUSHING  AND  GRINDING  PRACTICE.  77 

the  Ivanhoe,  the  compensating- weight  rings  are  highly  thought 
of,  and  much  has  been  published  about  them,  but  at  the  next 
mine  visited,  I  was  informed  that  the  compensating- weight  rings 
had  been  thrown  out,  as  having  proved  of  no  advantage  whatever. 
At  the  next  mine  I  was  told  the  old  original  8-ft.  pans  first  intro- 
duced were  the  best  pans  on  the  field,  and  these  8-ft.  pans 
are  being  adopted  for  the  most  recent  plants.  There  is  need  for 
authoritative  work  to  be  done  in  this  matter,  and  I  hope  that 
Messrs.  Klug  and  Taylor  will  continue  their  valuable  investigations 
into  the  subject. 

A  curious  result  of  the  introduction  of  electric  power  is  that 
ball-mills  (No.  5)  formerly  rated  at  17  to  24  h.p.  (steam)  are 
now  rated  at  40  h. p.  (electric).  Asa  little  over  200  h.p.  (steam)  is 
running  nine  of  these  mills  at  Kalgoorlie  with  three  fans  and  all 
the  shafting,  and  as  24  h.p.  is  about  the  highest  figure  indicated 
for  a  No.  5  Krupp  mill  with  full  charge  and  running  10%  over 
normal  speed  and  including  shafting,  etc.,  there  must  either  be 
a  lamentably  poor  efficiency  of  the  electric  motors  or  else  the 
electric  rating  is  inaccurate. 


PANS  V.  TUBES 

(August  4,  1906) 

The    Editor: 

Sir — It  has  occurred  to  me,  in  the  case  of  many  of  the  contro- 
versies over  the  respective  merits  of  grinding  pans  and  tube-mills, 
that  no  real  basis  for  argument  would  be  left  if  more  attention 
were  paid  to  defining  the  work  to  be  performed  by  each  machine. 
For  instance,  is  total  sliming  of  the  ore  the  principal  consideration, 
or  is  sliming  only  to  be  the  final  stage  in  the  crushing  process? 

In  the  Transvaal,  total  sliming — or  at  least  total  fine  grinding — 
of  the  stamp-mill  product  seems  to  be  the  desired  end,  while  in 
Kalgoorlie  stamp-mill  practice  total  sliming  is  wanted  only  after 
a  preliminary  concentration  has  been  effected.  Both  grinding-pans 
and  tube-mills  are  in  use  here,  and  each  fills  satisfactorily  its  own 
position  in  the  -scheme  of  treatment.  The  introduction  of  the 
grinding  pan  into  the  milling  practice  of  Western  Australia  was 
undoubtedly  due,  in  the  first  place,  to  a  desire  to  lower  the  treat- 
ment costs  in  wet-crushing  mills,  which  were  using  the  bromo- 
cyanide  process  on  sulpho-telluride  ores.  Its  success  in  this 
particular  function  has  led  to  its  development  as  a  grinding  mach- 
ine pure  and  simple  on  many  different  classes  of  ores.  The  con- 
ditions which  introduced  the  pan  were : 

1.  A  high  consumption  of  a  high-priced  chemical,  namely, 
bromo-cyanide. 

2.  The  knowledge  that  in  this  respect  expenditure  could  be 
most   easily  reduced   by   eliminating   by   concentration   as   much 
of   the   gold    as    possible   before   treatment    with   bromo-cyanide. 

3.  An  ore,  the  valuable  portion  of  which  was  most  susceptible 
to  sliming. 

4.  The  necessity  of  reducing  the  crushed  ore  from  the  stamps, 
to  a  size  which  would  free  the  mineral  particles  for  concentration, 
with  the  creation  of  a  minimum  percentage  of  slime. 

These  conditions  seem  somewhat  contradictory,  inasmuch 
as  good  concentration  practice  demands  that  the  mineral  be 
saved  in  as  coarse  a  condition  as  possible,  while  on  the  other  hand 
a  high  extraction  from  the  roasted  concentrates  demands  that  all 
mineral  particles  be  crushed  sufficiently  fine  to  free  them  from 


PANS  v.  TUBES.  79 

enclosure  in  gangue  material.  It  is,  however,  this  very  conflict 
of  demands  which  has  made  a  place  for  the  grinding  pan,  the 
construction  and  operation  of  which  renders  it  possible  to  regulate 
with  some  accuracy  the  size  of  the  product  which  it  discharges. 

While  stage  grinding,  as  a  preliminary  to  concentration,  is 
the  work  for  wrhich  the  pan  was  originally  introduced,  its  field  of 
usefulness  is  by  no  means  confined  to  this  particular  duty.  Its 
efficiency  as  a  fine  grinder  is  being  steadily  demonstrated,  and 
the  limit  to  which  fine  grinding  in  pans  can  be  carried  is  not  yet 
in  sight. 

In  regard  to  sliming  of  the  total  stamp-mill  product,  it  seems 
by  no  means  settled  whether  stage  grinding  in  pans  with  final 
sliming  in  tube -mills,  will  not  prove  more  economical  than  direct 
sliming  of  the  whole  product  in  tube-mills.  There  is  no  doubt, 
however,  that  as  an  adjunct  to  a  stamp-mill  for  the  purpose  of 
giving  increased  efficiency  to  the  stamps  by  allowing  the  use  of 
coarser  screens,  the  field  for  both  these  machines,  used  in  combina- 
tion with  each  other,  is  a  wide  one. 

It  is  the  successful  development  of  the  grinding  pan  which 
has  enabled  the  wet-crushing  mills  at  Kalgoorlie  to  survive  the 
increasing  competition  of  the  dry-crushing  and  roasting  mills; 
and  it  has  been  the  chief  factor  in  increasing  output  and  decreasing 
costs  of  the  stamp-mills  at  the  quartz  mines  outside  of  Kalgoorlie. 

D.  P.  MITCHELL. 

Kalgoorlie,  June  9/1906. 


ZINC  DUST  V.  SHAVING 

(August  18,  1906) 

The  Editor: 

Sir: — During  the  last  few  years  I  have  had  occasion  to  visit 
many  cyanide  plants  in  different  parts  of  the  country,  and  have 
noted  with  great  interest  the  methods  employed  in  different 
sections.  While  in  the  Black  Hills  a  few  years  ago  I  observed  with 
great  satisfaction  the  apparent  success  of  zinc-dust  precipitation 
and  noticed  with  what  economy  in  labor  great  volumes  of  solution 
were  handled.  The  question  arises  in  my  mind,  Why  is  zinc-dust 
precipitation  not  more  universally  employed?  All  cyanide  opera- 
tors are  well  aware  of  the  great  amount  of  labor  necessary  to  keep 
zinc-boxes  properly  dressed  and  in  good  working  order,  to  say 
nothing  of  the  labor  involved  in  the  monthly  or  bi-monthly  clean- 
up. In  point  of  economy  in  labor,  zinc-dust  precipitation  certainly 
has  the  advantage  over  precipitation  on  zinc-shavings.  If  it  is 
all  that  could  be  desired  in  other  respects,  why  would  it  not  be 
economy  to  design  all  plants  of  moderate  size  with  this  process? 

I  think  a  discussion  of  the  subject  by  those  employing  the 
process,  giving  figures  as  to  cost  of  installation  and  operation, 
efficiency,  etc.,  would  be  read  with  great  interest  by  cyanide 
operators. 

CYANIDE  MAN. 

Goldfield,   Nev.,  July   28,  1906. 


Zinc-dust  precipitation  in  cyanide  work  possesses  distinct 
advantages  over  zinc-shaving,  and  has  been  employed  with  marked 
success  at  the  cyanide  plants  of  the  Homestake  Company  in  the 
Black  Hills.  This  process  was  evolved  there  after  diligent  study, 
but  all  the  details  have  never  been  given  to  the  public,  and  it 
is  possible  that  the  success  of  the  process  at  the  Lead  City  plants 
may  depend  upon  some  important  trick  of  manipulation  which 
the  management  wishes  to  conceal.  Many  attempts  have  been 
made  to  use  the  process  at  other  plants,  but  without  success. 
It  would  be  difficult  to  assign  the  cause  for  this  failure.  It  may 
be  due  to  the  reluctance  of  operators  to  supplant  a  simple  and 


ZINC  DUST  v.  SHAVING.  81 

reliable  process  for  one  comparatively  complicated  and  untried; 
buc  it  would  seem  to  be  due  in  some  instances  to  unfavorable  con- 
ditions for  precipitation,  or  it  may  be  altogether  due  to  having 
missed  the  one  feature  essential  to  success,  as  known  only  to 
the  Homestake  operators.  The  reason  for  the  continued  popularity 
of  zinc-shaving  is  obvious.  The  process  is  simple  and  appeals 
to  the  average  intelligence.  We  join  with  our  correspondent 
in  his  wonderment  at  the  slow  introduction  of  zinc-dust,  and 
venture  to  predict  that  as  soon  as  the  process  gets  a  fair  start 
and  the  principles  of  its  use  are  better  understood,  it  will  easily 
supersede  the  cumbersome  method  in  vogue  at  the  present  time. 
We  shall  be  glad  to  publish  the  views  of  cyaniders  on  this  subject.— 
EDITOR. 


THE  TREATMENT  OF  DESERT  ORES 

(August  25,  1906) 

The  Editor: 

Sir — I  have  been  interested  in  the  discussion  by  Mr.  Bosqui 
and  Mr.  Hunt  relative  to  the  treatment  of  desert  ores.  As  I  have 
recently  been  required  to  devise  a  method  of  treatment  for  the  ore 
of  one  of  the  mines  near  the  Combination,  at  Goldfield,  the  follow- 
ing may  be  of  interest. 

The  material  is  typical  of  the  Goldfield  district,  but  was  the 
lower  grade  'milling  ore,'  averaging  about  $20  per  ton.  When 
the  samples  were  brought  to  the  laboratory  I  was  requested  to 
make  'amalgamation,  concentration,  and  cyanide  test' to  determine 
the  best  possible  extraction  obtainable.  The  test  gave  the  follow- 
ing results:  Recovered  by  amalgamation,  32%;  by  concentra- 
tion, 16.5%;  and  by  cyanidation  of  tailing,  46.5%,  making  a 
total  recovery  of  95  per  cent. 

The  concentrate  was  very  high-grade — being  over  $500  per 
ton — and  represented  -J%  by  weight  of  the  ore  taken.  After 
completing  this  test,  I  decided  to  try  direct  cyaniding  of  the  ore 
after  dry-crushing  the  whole  of  it  to  100-mesh,  with  the  result 
that  I  obtained  94%  extraction.  After  confirming  these  results 
by  further  tests,  I  recommended  the  following  general  method 
of  treatment:  Dry-crushing  to  12  or  16-mesh,  fine  grinding  in  tube- 
mills  with  cyanide  solution  to  100-mesh,  agitation,  and  filter- 
pressing. 

The  direct  treatment  of  this  ore  by  cyanide  would  have  many 
advantages  over  the  usual  custom  of  amalgamation  and  concen- 
tration followed  by  cyaniding.  In  the  first  place  water  is  very 
scarce;  in  the  ordinary  stamp-mill  practice  water  is  used  in  the 
ratio  of  from  four  to  seven  parts  by  weight  to  one  of  ore.  In 
following  the  idea  suggested  above,  it  would  be  necessary  only 
to  use  a  sufficient  amount  of  water  as  cyanide  solution  to  get  the 
best  results  from  the  tube-mill,  and  agitation  tanks,  and  for  wash- 
ing in  the  filter-presses.  According  to  Mr.  Butters,  El  Oro  practice 
shows  that  the  proportion  of  water  to  ore  used  in  tube-mills  should 
be  one  to  one,  or  less,  to  obtain  the  greatest  efficiency.  The 
plant  would  cost  much  less  to  install  than  the  usual  stamps  and 


THE  TREATMENT  OF  DESERT  ORES.  83 

concentrators  with  sand' and  slime  cyanide-annex;  and,  requiring 
but  one  crew  of  men,  it  would  reduce  the  operating  costs  materi- 
ally. I  doubt  the  advisability  of  treating  the  majority  of  ores 
in  both  sand  and  slime  plants;  such  plants  in  my  opinion  being 
suitable  only  to  tailing  piles  where  the  crushing  has  already  been 
done.  In  most  ores  if  a  plant  is  necessary  to  treat  the  slime 
when  crushing  coarse,  it  will  pay  to  slime  everything  and  treat 
altogether — thus  combining  all  the  work  in  one  plant  with  one 
crew.  Nor  do  I  believe  in  the  other  practice — except  in  rare 
cases — of  crushing  all  the  ore  to  a  200-mesh  slime.  Those  who 
have  had  to  operate  filter-presses  or  filtering  devices  realize  the 
difficulty  of  filtering,  washing,  and  removing  cakes  of  200-mesh 
slime;  while  if  all  the  ore  is  crushed  to  100  mesh,  agitated  as  one 
product,  and  filter-pressed,  the  extraction  is  not  materially  re- 
duced, save  in  exceptional  cases  and  the  cakes  can  be  made  thicker 
and  dryer,  and  are  easily  washed  and  removed.  In  fact,  some 
of  the  new  presses  are  so  constructed  that  material  of  this  kind 
can  be  filtered,  washed,  and  sluiced  out  automatically  without 
entailing  the  expense  of  opening  the  presses  between  each  change. 
Tnis  is  not  possible  with  a  very  fine  slime,  which  becomes  as  tena- 
cious as  India  rubber  and  must  be  almost  chiseled  from  the  cloths. 
In  the  majority  of  cases  the  mill  clean-up  will  show  a  greater 
extraction  than  if  all  is  crushed  to  pass  200-mesh;  the  possible 
exceptions  are  sulphides  or  perhaps  a  clean  silicious  ore,  free  from 
argillaceous  material. 

Mr.  Bosqui,  in  advocating  wet  crushing  and  amalgamation, 
mentions  the  "great  advantage  of  being  able  to  secure  daily  from 
plates  50%  of  the  extraction  obtained  from  $50  ore,  as  compared 
with  waiting  for  the  tedious  monthly  or  bi-monthly  clean-up  in  a 
cyanide  plant."  I  confess  that  I  cannot  see  this  advantage. 
Crushing  60  to  75  tons  per  day  and  recovering  $25  per  ton  would 
be  but  $1,875  per  day  at  most,  and  surely  he  would  not  make  a 
melt  every  day  for  that  amount.  A  bi-monthly  clean-up  would 
amount  to  but  $28,000,  which  is  not  an  unusual  clean-up  even  in 
our  California  mills.  A  cyanide  plant,  if  properly  designed, 
can  be  roughly  cleaned  up  every  ten  days  without  any  great 
inconvenience;  to  be  followed  by  a  complete  clean-up,  say  once  a 
month.  I  must  agree  with  Mr.  Hunt  regarding  the  practicability 
of  crushing  dry  to  any  required  fineness,  as  instanced  in  cement 
mills,  but  that  is  not  necessary.  It  is  my  belief  that  the  time  will 


84  RECENT  CYANIDE  PRACTICE. 

soon  come  when  nearly  "every  new  modern  mill  operating  upon  a 
logical  basis"  on  the  deserts  will  be  so  constructed  that  crushing 
to  10  or  16  mesh  will  be  done  dry  by  breakers  and  rolls  or  ball- 
mills,  and  the  whole  product  will  then  b«  mixed  with  cyanide 
solution  of  a  strength  sufficient  to  obtain  the  highest  extraction 
and  passed  through  tube-mills  or  some  other  device  to  reduce 
to  a  fineness  of  100  mesh;  that  the  product  will  all  be  agitated 
together  and  passed  to  filter-presses  so  constructed  as  to  permit 
of  automatic  discharging. 

The  objection  to  dust,  I  think,  will  be  overcome  as  it  is  in  the 
cement  mills  of  Europe,  where  the  laws  compel  the  installation 
of  exhaust-fans  and  dust-collectors.  In  a  plant  such  as  I  have 
roughly  outlined,  the  dust  could  be  conveyed  by  pipes  connected 
with  an  exhaust-fan  to  a  hopper,  where  a  spray  of  cyanide  solution 
would  collect  and  carry  it  to  be  mixed  with  the  tube-mill  product. 
Such  an  arrangement  would  be  efficient,  and  the  cost  of  installing 
and  operating  would  be  trifling. 

Another  point  which  I  think  is  generally  overlooked  is  that 
the  coarse  gold  in  any  ore  when  subjected  to  the  grinding  action  of 
the  tube-mill  or  any  other  machine  necessary  to  pass  it  through 
a  100-mesh  screen,  will  cease  to  be  coarse  gold.  All  of  us  know 
how  brittle  gold  becomes  even  upon  rolling,  as  is  seen  in  assaying 
bullion  when  rolling  out  the  cornets,  which,  unless  repeatedly 
annealed,  will  break  to  pieces.  This  same  action  occurs  in  grind- 
ing the  ore  and  is  aided  by  the  sand  grit,  so  that  by  the  time 
the  ore  passes  100  mesh,  practically  every  particle  of  gold  is  a  very 
fine  scale,  a  most  ideal  condition  for  cyanide  attack. 

Crushing  to  10  or  16  mesh,  no  matter  how  hard  the  rock, 
is  done  cheaper  in  breaker  and  rolls  dry,  than  with  breakers  and 
stamp-mills  wet.  The  cost  of  installation  per  given  capacity  is 
less,  and  in  desert  regions,  where  water  is  of  itself  such  a  problem, 
the  dry-crushing  method  must  appeal  to  both  the  manager  and  the 
metallurgist. 

I  think  it  is  becoming  generally  recognized  that  fine  grinding  of 
the  whole  product  to  100  mesh  increases  the  profits,  and  when 
this  is  so  I  do  not  think  amalgamation  should  play  any  part  in 
the  process,  except  possibly  in  very  rich  (over  $100)  coarse  gold 
ores.  The  stamp-mill  as  an  amalgamator  and  when  crushing  to 
30  or  40  mesh  has  long  held  its  place  in  the  first  rank,  and  for 
that  purpose  can  hardly  be  replaced.  But  its  success  in  this. 


THE  TREATMENT  OF  DESERT  ORES.  85 

line  seems  "by  the  compelling  force  of  custom"  to  lead  metallur- 
gists to  its  adoption  in  all  cases.  But  new  conditions  have  been 
presented.  We  no  longer  want  a  30  or  40-mesh  product,  but  a 
100-mesh.  Therefore  let  us  adopt  the  machines  best  suited  to 
these  new  conditions. 

LOCHIEL  M.  KING. 
Oakland,  August  1. 


CYANIDE  NOTES 
BY  E.  A.  H.  TAYS 

(September  1,  1906) 

Successful  cyaniding  depends  on  two  things:  A  working 
knowledge  of  the  process,  and  common  sense.  A  certain  treatment 
may  be  successful  at  one  camp  and  fail  at  another;  in  fact,  the 
treatment  successful  with  ore  from  one  level  of  a  mine,  may 
fail  with  the  ore  from  another  level  of  the  same  mine.  Conse- 
quently, to  be  successful,  the  cyanider  must  be  ever  alert. 

Another  thing  he  must  bear  in  mind,  and  that  is  never  to 
despise  future  possibilities.  I  call  to  mind  a  personal  experience. 
We  were  treating  with  fair  success,  a  refractory  lot  of  tailing 
of  high  value,  and  because  the  mill-tailing  was  a  little  poorer  than 
that  from  the  cyanide  plant,  we  ran  all  of  it  down  the  arroyo, 
as  being  worthless  to  us.  Five  years  later,  at  the  same  plant, 
I  treated  at  a  profit,  tailing  carrying  but  one-half  the  values  of  that 
which  ran  into  waste  five  years  before. 

We  all  recognize  that  oxidation  of  the  charge  during  treatment 
is  desirable  in  securing  high  extraction;  but,  so  far,  no  economical 
method  of  obtaining  this  condition  has  been  devised.  I  refer  to 
the  leaching  of  ordinary  sand  charges,  for  the  agitated  charges 
of  slime  are  readily  oxidized.  It  is  generally  conceded  that  in  a 
vat  charged  with  sand,  when  drained,  the  charge  is  affected  by 
the  oxygen  of  the  atmosphere  to  a  depth  of  but  a  foot  or  two  below 
the  surface.  From  experiments  and  accidental  discoveries,  I 
am  led  to  believe  that  such  charges  are  affected  to,  or  nearly  to, 
the  bottom;  time  being  the  only  essential. 

I  call  to  mind  a  small  plant  treating  from  800  to  1,000  tons 
per  month,  it  being  an  old  plant  remodeled.  The  material  treated 
was  a  tailing  from  a  stamp-mill,  consisting  of  at  least  25%  clay 
slime;  and,  at  best,  only  80%  could  be  extracted  from  it.  It  should 
have  been  arranged  to  separate  the  slime  from  the  sand,  in  order 
to  treat  each  separately,  and  this  could  have  been  done  economi- 
cally; but,  as  the  plant  was  working  to  good  advantage,  it  was 
deemed  best  to  make  no  change.  The  treatment  was  designed 
to  discharge  one  vat  (about  36  tons)  per  day,  and  as  there  were 
ten  vats,  each  vat  was  given  a  ten  days'  treatment,  although 


CYANIDE  NOTES.  87 

the  engineer  told  me,  in  turning  over  the  plant,  that  full  extraction 
was  made  in  seven  days.  After  a  month  or  two  some  experiments 
were  made,  and  it  was  found  that  as  good  results  as  could  be 
obtained  from  the  material  treated  could  be  obtained  in  five  days ; 
and,  of  course,  after  verifying  these  results,  it  was  decided  to  double 
the  output,  as  this  increased  the  running  expenses  but  little. 

While  we  were  waiting  for  extra  supplies  (two  months)  the 
five-day  system  was  installed,  and  practice  upheld  the  experi- 
ments, as  long  as  we  had  an  excess  of  vat  capacity.  When  every- 
thing was  ready  to  double  the  output,  and  every  vat  was  put 
regularly  into  commission,  our  extraction  dropped  off  from  6  to 
8%  and  continued  low  all  one  month,  before  the  trouble  was  de- 
tected. 

The  treatment  was  as  follows: 

1.  Charge  vat  with  sand 8   hours 

2.  Charge  strong  solution  (0.2%)  from  below,  valve  half  open 

and  let  soak 14 

3.  Discharge,  valve  wide  open,  until  solution  titrated  0.1%, 

then  charge  weak  solution  (0.1%)  on  top  and  let  run.  .      12 

4.  Charge  allowed  to  drain 12 

5.  Strong  solution  charged  from  above,  until  vat  filled,  when 

valve    was    opened,    and   when   the    escaping   solution 
titrated,  0.1%,  weak  solution  was  run  on  six  hours  12 

6.  Charge  allowed  to  drain 18 

7.  Strong  solution  charged   (from  above)  until  full,  and  left 

to  saturate 6 

8.  Solution  drained  off  and  when  titrated  0.1%,  weak  solution 

was  fed  on  top,  feeding  and  draining  at  same  time 12 

9.  Let   drain  two  hours,   when  seven  tons  fresh  water  were 

run  on  from  top  and  charge  let  drain 18 

10.      Sample  and  discharge  tailing 8 

Total 120   hours 

This  treatment  gave  us  good  results  in  five  days,  during  full 
charge  experiments,  when  we  had  extra  vats;  but  when  all  the  vats 
were  put  into  commission  as  already  stated,  the  extraction  dropped 
as  much  as  eight  per  cent. 

In  going  over  the  treatment  step  by  step,  everything  checked 
up  to  the  ninth  step.  It  was  found  that  while  our  scheme  called 
for  the  treatment  indicated,  when  we  had  vats  to  spare,  the  boys 
let  the  charge  drain  (oxidize,  in  fact),  up  to  within  the  14  hours 
necessary  to  fill  the  water- wash  and  drain  dry  enough  to  discharge, 
the  vats  remaining  dry  about  four  days  before  the  water-wash 


88  RECENT  CYANIDE  PRACTICE. 

was  run  on.  This  long  period  of  rest  allowed  the  latent  reaction 
of  oxidation  to  develop  fully,  and  when  the  water  was  run  on  it 
readily  took  into  solution  the  dissolved  metals  still  in  the 
tailing. 

After  this  discovery,  the  treatment  was  modified,  as  follows: 

1.  Charge  vats  with  material 10    hours 

2.  Charge  strong  solution  (0.2%)  from  below  at  one-half  valve 

capacity,  and  let  soak 14 

3.  Discharge  solution,  valve  wide  open,  and  at  end  of  second 

hour,  feed   (on  top)  weak  solution   (0.1%);  valve  half 
open 12 

4.  Let  charge  drain,  valve  wide  open 12 

5.  Charge  strong  solution  from  top,  and  let  soak 6 

6.  Discharge,   valve  wide  open,   and  at  end  of  second  hour, 

charge  (on  top)  weak  solution;  valve  half  open 12 

7.  Let  charge  drain 18 

8.  Charge  weak  solution  from  top,  valve  wide  open,  and  let 

soak 6 

9.  Let  charge  drain  and  oxidize 62 

10.  Charge  fresh  water  from  top,  until  vat  fills,  and  let  soak  .  .        3 

11.  Open  valve  wide,  letting  charge  drain;  this  wash  going  to 

storage- vat  leading  to  zinc-boxes 13 

12.  Sample  and  discharge  tailing .      12 

Total 180    hours 

This  treatment  gave  good  normal  results;  and,  as  a  charge  was 
run  through  in  7^  days,  it  still  gave  us  a  total  of  1,500  tons  per 
month,  instead  of  1,000  tons  under  former  treatment. 

I  firmly  believe  now  that  oxidation  takes  place  clear  to  the 
bottom  of  a  vat  full  of  sand,  the  vat  having  been  filled  with  water 
and  this  then  allowed  to  drain  off,  from  the  bottom.  When  full 
of  water,  the  interstices  are  occupied  by  the  water,  the  sand 
settling  and  packing  as  close  as  possible.  As  the  water  drains  off, 
these  interstices  empty  and  form  a  vacuum,  which  naturally  fills 
with  air;  the  pressure  of  this  being  ample  to  fill  the  lower  voids, 
as  the  water  recedes.  Once  the  interstices  are  filled  with  air, 
the  chemical  reactions  that  take  place  cause  a  practical  oxidation 
to  set  in,  if  time  be  allowed;  and  it  is  probable  that  80%  of  this 
reaction  takes  place  within  60  hours.  That  the  interstices  in 
the  charge  do  fill  with  air  is  proved  by  the  fact  that  in  running 
water  on  to  a  charge,  much  ebullition  takes  place,  and  for  half 
an  hour  or  more  after  the  charge  is  covered  with  water;  many 
air-holes  forming  all  over  the  top  of  the  charge. 


CYANIDE  NOTES.  89 

Another  proof  that  chemical  reaction  takes  place  in  a  charge 
treated  as  outlined,  and  then  left  to  drain  three  or  four  days 
is  (from  my  ow,n  tests)  that  if  a  water-wash  be  run  through  imme- 
diately, it  will  show  but  a  few  cents  per  ton;  whereas,  if  the  water- 
wash  be  run  through  several  days  after  the  charge  has  been  allowed 
to  drain,  it  will  carry  from  $1.50  to  $2  per  ton. 

Several  years  ago  I  discovered  that  newly  turned  zinc,  if 
the  shavings  where  stored  were  exposed  to  air,  was  necessary  for 
perfect  precipitation.  Later,  I  have  learned  that  solutions  running 
through  the  zinc-boxes  should  not  be  too  strong  in  cyanide,  if 
a  product  high  in  the  precious  metals  be  desired.  When  the  solu- 
tions run  0.1%  or  over,  the  reaction  set  up  is  so  violent,  that  a 
larger  proportion  of  zinc  is  destroyed  (oxidized)  than  is  necessary, 
the  resulting  slime  (auro-cyanide)  being  low  in  gold  and  silver 
and  high  in  zinc. 

With  weak  solutions  the  reaction  is  normal,  and  metallic 
zinc  is  destroyed  in  proportion  to  the  values  in  the  solution;  and 
the  resultant  slime  is  high-grade.  I  have  secured  slime  running 
$30,000  per  ton  and  high  in  zinc,  requiring  acid  treatment ;  whereas, 
the  next  month,  on  the  same  grade  of  ore,  slime,  low  in  zinc, 
requiring  no  acid  treatment,  and  carrying  $57,000  gold  per  ton, 
was  obtained,  simply  by  not  allowing  the  solutions  to  get  beyond 
a  certain  strength,  say  0.05%.  For  this  reason,  my  practice  has 
been,  of  late  years,  to  run  all  solutions  and  water-washes  into 
a  common  vat,  the  mixed  solutions  from  which  are  run  to  the 
zinc-boxes.  When  the  solution  is  above  0.05%  in  cyanide  it 
can  be  run  through  the  zinc-boxes  a  little  slower;  and  when  below 
0.05%,  a  little  faster,  to  obtain  the  normal  results.  Should  the 
solution  be  very  low  in  cyanide,  say  0.01%,  and  yet  rich  in  metals, 
a  little  cyanide  can  be  added  to  the  head  box  in  each  row,  if  it 
is  found  that  solutions  of  0.01%  strength  do  not  precipitate  nor- 
mally. 

In  the  clean-up  it  is  good  practice  to  return  all  zinc,  staying 
on  a  40-mesh  screen,  to  the  precipitating-boxes.  This  zinc  should 
be  kept  covered  with  a  weak  KCy  solution  until  returned  to  the 
boxes.  This  prevents  the  violent  oxidation  that  sets  in  under 
exposure  to  the  atmosphere. 


COPPER  AND  CYANIDE  SOLUTIONS 

(September  1,  1606) 

The    Editor: 

Sir — I  am  on  my  way  back  to  the  mines  again.  Just  had  a. 
letter  from  my  cyanide  man,  which  says  we  are  getting  a  fearful 
lot  of  copper  in  the  zinc-boxes.  Will  you  send  me,  to  my  address 
at  the  mine,  anything  that  has  been  printed  of  late  on  this  sub- 
ject, for  all  I  know  seems  very  meagre  on  the  matter. 

R.  B.  S. 

New  Orleans,  August  14,  1906. 

The  presence  of  copper  in  ores  .causes  decomposition  or  loss 
of  cyanide  when  they  are  treated  by  the  cyanide  process,  especially 
when  it  occurs  in  the  form  of  carbonate,  each  pound  of 
copper  dissolved  combining  with  about  four  pounds  of  potassium 
cyanide.  A  further  trouble  is  met  in  the  precipitation  by  means 
of  zinc-shaving,  owing  to  the  tendency  of  the  copper  to  form 
a  firm  metallic  coating  on  the  surface  of  the  shaving  when 
the  cyanide  solutions  used  are  comparatively  weak.  With  stronger 
solutions  less  copper  is  precipitated,  and  then  in  a  more  loose  and 
spongy  form,  which  does  not  prevent  the  deposition  of  gold  and 
silver.  The  experiments  of  Von  Oettingen  (Journal  Chem.  & 
Met.  Soc.  South  Africa,  Feb.,  1899,  and  Proceedings,  Vol.  II,  pp. 
557-570),  and  of  Christy  (Transactions  A.  I.  M.  E.,  Sept.  1899), 
show  that  the  difference  of  potential  between  zinc  and  copper  is 
greatest  in  very  weak  solutions  of  KCN,  becoming  very  small  in 
strong  solutions.  This  is  brought  out  in  a  graphic  manner  in 
Prof.  Christy's  Fig.  19.  Experiments  and  working  results  quoted 
by  Sharwood  (Proceedings  13th  Convention  California  Miners' 
Association,  pp.  209,  210,  MINING  AND  SCIENTIFIC  PRESS,  April 
29,  May  6  and  13,  1905)  show  that  much  more  of  the  copper  present 
was  thrown  down  from  weak  than  from  stronger  solutions.  See 
also  Browne  (MINING  AND  SCIENTIFIC  PRESS,  Jan.  24,  1903.) 

Whether  it  will  pay  best  to  use  stronger  solutions,  or  to  add 
cyanide  before  precipitating,  or  to  substitute  some  other  method 
of  treatment  or  of  precipitation,  will  depend  on  a  number  of  cir- 
cumstances. This  is  discussed  by  Julian  and  Smart  ('Cyaniding  Gold 
and  Silver  Ores,'  p.  209).  The  dipping  of  zinc-shaving  in  a  solution 


COPPER  AND  CYANIDE  SOLUTIONS.  91 

of  lead,  patented  by  MacArthur,  was  intended  to  overcome  the 
difficulty  caused  by  copper  in  the  zinc-box.  Another  patented 
process  (Porter's)  is  said  to  be  used  at  the  Bagdad-Chase  mine, 
the  gold  being  precipitated  by  zinc  shaving  and  the  copper  after- 
ward removed  by  prolonged  treatment  with  zinc-dust  and  ammonia. 
This  was  described  in  the  MINING  AND  SCIENTIFIC  PRESS  of  May 
20,  1905.— EDITOR. 


CJANIDE  PRACTICE  WITH  THE  MOORE 
FILTER— 1 

BY  R.  OILMAN  BROWN 

(September  1,  1906) 

The  plant,  of  which  the  following  is  a  description,  was  designed, 
erected,  and  brought  to  satisfactory  operation  during  the  years 
1904-5.  Much  of  the  burden  of  the  preliminary  investigation 
and  construction  fell  naturally  upon  the  shoulders  of  Mr.  Theodore 
J.  Hoover,  superintendent  of  the  company,  for  which  the  writer 
was  general  manager.  During  the  progress  of  the  work  a  large 
mass  of  data,  experimental  and  practical,  was  collected,  which 
the  two  of  us  had  planned  to  collate  and  publish  in  collaboration. 
This  was  all  lost  in  the  San  Francisco  fire.  This  paper  and  draw- 
ings have  been  prepared,  largely  from  memory,  but  with  the  valu- 
able assistance  of  the  private  notes  of  Mr.  E.  H.  Nutter,  who  from 
his  position  as  mechanical  engineer  and  later  superintendent  for 
the  Standard  Co.,  had  been  fully  in  touch  with  the  plant  from  the 
first. 

Ever  since  the  installation,  in  the  early  '90s,  of  the  first 
cyanide  plant  at  the  Standard  mine,  at  Bodie,  California,  under 
the  initiative  of  Mr.  Thos.  H.  Leggett,  the  treatment  of  the  slime 
has  been  a  problem  of  growing  importance.  The  earliest  practical 
attempt  to  solve  it  was  in  the  nature  of  an  evasion;  namely,  to 
break  the  caked  slime  from  the  ponds  with  a  disc-harrow  and  mix 
it  with  sand.  Apart  from  the  cost,  which  came  to  an  additional 
30c.  or  more  per  ton  on  the  whole  tonnage,  including  the  sand, 
the  coarse  material  was  only  sufficient  for  the  dilution  of  a  portion 
of  the  slime  product.  Besides,  this  method  took  no  advantage  of 
the  fact  that  by  agitation  the  slime  would  yield  a  higher  extraction 
in  a  shorter  period.  For  want  of  a  better  way,  the  practice  was 
continued  for  a  time,  as  the  only  way  of  preventing  the  congestion 
of  the  tailing  ponds  with  untreatable  slime.  But  active  experi- 
ments were  made  in  other  directions. 

Agitation  and  decantation  were  discarded  because  of  the 
flocculent  character  of  much  of  the  slime,  that  would  not  settle 
in  72  hr.  to  over  15%  solids.  '  Filter-pressing  was  tried  and  aban- 


THE    MOORE    FILTER— I.  93 

doned,  because  an  eighth  of  an  inch  of  pure  slime  would  make  the 
cloths  impervious,  even  under  120-lb.  pressure;  and  even  if  the 
slime  was  mixed  with  fine  sand,  the  filtering  was  so  slow  that  the 
sand  settled  out  in  the  chambers,  with  the  same  result. 

Dehydration  of  dry  slime  by  roasting  made  both  filtering  and 
decantation  possible,  but  with  lower  extraction  and  high  cost; 
moreover,  it  was  not  applicable  to  the  direct  treatment  of  the  wet 
product  from  a  stamp-mill.  More  than  one  method  of  filtration 
in  vats  during  agitation  was  tried  and  discarded.  In  the  summer 
of  1903  the  first  crude  tests  with  the  Moore  method  were  made, 
with  no  brilliant  results.  Later  a  personal  investigation  of  the 
plant  at  Mercur  made  clear  the  inherent  advantages  of  the  method, 
while  at  the  same  time  it  exposed  certain  mechanical  deficiencies. 
An  experimental  plant  of  half  a  ton  capacity  was  installed  at  Bodie 
and  from  the  first  the  results  were  good.  Such  was  our  success 
that  by  the  middle  of  the  winter  we  decided  to  apply  it  to  all  the 
tailing  from  the  Standard  mill.  In  designing  the  plant  every 
care  was  taken  to  avoid  the  defects  of  the  Mercur  plant,  but  not- 
withstanding this,  several  months  were  consumed,  after  the  plant 
was  nominally  completed,  in  alteration  and  modification,  the  major 
part,  let  it  be  noted,  being  in  details  outside  of  the  Moore  process 
proper.  By  the  middle  of  1905  operations  had  become  fairly 
regular  and  the  profit  for  the  whole  year  amounted  to  more  than 
half  the  cost  of  the  plant. 

The  ore  consists  of  quartz,  iron  oxides,  and  clay,  the  last  com- 
ing from  the  decomposition  of  feldspar  in  the  country  rock.  At 
times  this  equals  50%  of  the  ore  and  as  an  average  can  be  taken 
at  33  J%.  The  gold  is  partly  coarse  and  partly  very  fine,  the  latter 
portion  amalgamating  badly,  to  such  an  extent  that  at  any  time 
fine  colors  can  be  panned  from  below  the  vanners.  The  propor- 
tion of  silver  is  high,  the  mill  bullion  being  worth  only  $10  to  $12 
per  ounce.  Altogether  it  is  a  difficult  ore  to  treat,  despite  the  total 
absence  of  all  minerals  ordinarily  classed  as  deleterious. 

In  conjunction  with  the  introduction  of  the  Moore  method 
weak  cyanide  solution  was  substituted  for  water  in  the  20-stamp 
mill  and  the  grade  of  the  plates  was  increased  from  1J  to  2£  in.  per 
foot,  in  order  to  cut  down  the  proportion  of  liquid  to  keep  the 
plates  clear.  This  steep  grade,  in  conjunction  with  the  hardening 
effect  of  the  cvanide  solution  on  amalgam,  has  diminished  the 


94  RECENT  CYANIDE  PRACTICE. 

extraction  by  free  milling  from  60  to  50%.  After  considerable 
experiment  the  strength  of  cyanide  solution  was  settled  at  two 
pounds  per  ton,  and  with  this  at  first  no  trouble  was  experienced 
with  the  plates,  but  of  late  the  lower  ones,  where  the  amalgam 
lies  thinnest,  have  shown  signs  of  wasting,  and  some  have  been 
renewed.  Possibly  this  can  be  lessened  by  using  Muntz  metal 
or  by  carrying  a  heavier  coating  of  amalgam.  Lime,  at  the  rate 
of  10  Ib.  per  ton,  is  added  to  the  ore  before  it  goes  to  the  crusher. 
After  passing  over  vanners,  the  pulp  is  raised  63  ft.  to  the  high- 
level  flume  for  conveyance  to  the  slime-plant,.  1,800  ft.  away. 
The  elevation  is  done  by  four  Frenier  sand-pumps,  in  series.  The 
three  lower  ones,  10  by  54  in.,  have  a  lift  of  16  ft.  4  in.  each;  the 
upper  one  is  8  by  48  in.,  and  has  a  lift  of  14  ft.  The  high  level 
flume  is  four  inches  wide  and  nine  inches  deep,  set  on  a  grade 
of  7/i6  in.  per  ft.;  the  pulp  carries  17  to  19%  solids  and  at  this 
grade  it  flows  freely  under  all  conditions  of  temperature.  A  grade 
of  5/ie  in.  was  found  insufficient,  particularly  in  cold  weather; 
a  broader  flume  was  also  found  to  give  trouble  by  accumulations 
of  sand.  When  received  at  the  slime-plant,  the  pulp  is  again 
raised  by  a  centrifugal-pump  to  the  cone-separators.  A  word 
regarding  the  two  methods  of  handling  pulp:  The  Frenier  pump, 
for  a  regular  flow  and  for  lifts  within  its  capacity,  is  most  satis- 
factory; the  consumption  of  power  is  nominal  and  the  wear  is 
confined  to  the  stuffing-box  at  the  discharge;  however,  it  requires 
more  attention  in  operation,  particularly  in  starting  or  stopping, 
and  a  great  deal  of  pains  in  erecting. 

The  re-grinding  is  done  in  a  5  by  22  ft.  trunnion  tube-mill 
of  Allis-Chalmers  make.  The  feed  is  from  the  under-flow  of  two 
cone -separators.  These  are  of  wood,  approximately  five  feet 
deep  and  with  60°  slope  of  side.  No  extra  solution  is  used 
to  affect  the  separation,  the  degree  of  which,  that  is  to  say  the 
proportion  of  overflow  to  underflow,  being  regulated  by  a  simple 
needle-valve  actuated  by  a  screw  and  hand-wheel  from  the  top. 
The  routine  test  for  separation  is  to  catch  the  overflow  on  a  150- 
mesh  screen  and  raise  the  needle-valve  until  no  material  is  held 
on  the  screen.  The  underflow,  containing  the  coarse  stuff  and  a 
certain  proportion  of  adhering  slime  passes  to  the  tube-mill,  being 
mixed  with  sand  and  slime  from  the  ponds,  automatically  fed  into 
the  stream.  The  outflow  from  the  mill  is  returned  to  the  cones. 
The  mill  makes  26  rev.  per  min.  The  pebbles  are  Greenland 


THE    MOORE    FILTER— I.  95 

concretionary  flints,  the  charge  being  about  12  tons  which  fills 
the  mill  a  short  distance  above  the  middle.  This  charge  seems 
to  be  the  best  for  grinding  and  most  economical  of  power,  but  the 
difference  is  not  great  and  the  charge  can  wear  to  half  this  quan- 
tity with  small  diminution  of  grinding.  The  attempt  was  early 
made  to  use  selected  pebbles  from  local  glacial  drift,  but  their 
irregularity  prevented  free  motion,  and  gave  a  high  wear  of  liners, 
with  increased  power  consumption.  The  insufficient  hardness 
also  of  the  pebbles  made  them  expensive. 

The  linings  originally  furnished  were  of  white  cast  iron,  secured 
in  place  only  by  the  arch  of  the  shell.  They  were  a  constant 
source  of  trouble  from  dropping,  and  their  life  was  short.  Soft- 
wood blocks  on  end,  six  inches  long,  were  next  tried.  There  was 
no  diminution  of  the  grinding,  but  besides  their  short  life — of 
about  10  days — they  introduced  an  unexpected  element  in 
excessive  foaming  of  all  the  solutions.  It  was  assumed  that  this 
was  due  to  a  saponification  of  the  wood  oils  by  the  alkali  in  the 
solution.  But  whatever  the  cause,  it  produced  an  overwhelming 
mass  of  suds,  overflowing  all  the  launders  and  covering  the  vats 
with  18  in.  to  2  ft.  of  foam.  Mountain  mahogany  was  tried  next, 
diminishing  this  trouble,  but  with  scarcely  a  longer  life.  Silex 
was  subsequently  used,  and  for  a  time  answered  well,  but  when 
partly  worn  there  was  continual  delay  from  replacing  worn-out 
blocks.  This  objection  was  entirely  aside  from  the  delay  of  four 
weeks  or  more  demanded  for  the  full  setting  of  the  cement  that 
held  the  lining  in  place.  The  continuation  of  the  use  of  silex 
meant  the  addition  of  a  second  tube-mill,  that  is,  the  duplication 
of  the  re-grinding  plant. 

Finally,  the  practice  settled  down  to  wrought-iron  plates 
for  liners.  These  are  |  by  8  in.,  cut  into  7  and  15-ft.  lengths,  and 
bolted  through  the  shell.  Some  of  the  plates  of  this  lining  would 
be  worn  through  in  90  days,  but  by  replacing  these  the  average 
life  came  to  over  100  days  and  the  duty  to  4,800  tons  of  sand, 
ground  to  200-mesh.  The  consumption  of  pebbles  was  15^  tons; 
reducing  this  to  pounds  per  ton,  the  lining  wear  was  2.44  Ib.  and 
the  pebble  consumption  6.47  Ib.  It  seems  likely  that  the  wear 
of  lining  and  pebbles  is  rather  a  function  of  time  than  of  tonnage 
and  in  any  case  it  is  certain  that  the  rate  of  wear  of  lining  at  least 
is  much  affected  by  the  manipulation  and  proportion  of  solid 
in  the  feed;  so  that  this  somewhat  anomalous  success  with  the 


96  RECENT  CYANIDE  PRACTICE. 

softer  lining  is  probably  in  a  measure  due  to  the  increased  skill  in 
adjusting  the  feed  to  the  mill.     It  is  to  be  noted  as  a  point  in 
favor  of  the  wrought  iron  that  there  is  little  waste,  as  it  can  be 
worn   down   thin   without   breaking.     Aside   from   this,    the   ease 
of  inserting  and  securing  the  straps — all  of  which  can  be  accom- 
plished in   10  hr. — was  the  determining  argument  for  their  final 
adoption.     The   power  for  the  mill  is   approximated  as   50   h.p. 
when  running  and  100  h.p.  at  starting.     The  maximum  grinding 
capacity    of    the    single    unit    has  not    been    definitely    reached, 
but  it  is  safe  to  place  it  at  60  tons  of   sand  per  24  hr.     This  makes 
the  duty  of  a  horsepower  month  36  tons.     At  normal  cost  of  electric 
power  in  California  the  power  cost  comes  to  17c.  per  ton;  at  the 
Standard  mine,  which  produces  its  own  power,  the  cost  is  5Jc. 
An   interesting   comparison   can   here  be  made   between   the   cost 
in  power  of  stamping  from  2^-in.  size  to  30-mesh    and  grinding 
from  30-mesh  to  200.     The  consumption  of  power  in  the  Standard 
mill  of  1,000-lb.  stamps  is,  for  stamping  alone,  28  h.p.     The  month- 
ly tonnage  is   1,800,  so  that  the  duty  of  one  horsepower-month 
is  64  tons.     The  reduction  of  linear  size  from  1\  in.  to  30-mesh 
is  given  in  the  ratio  2.5:0.025  or  100:1.       For  the   tube-mill  the 
ratio  between  feed  and  product  is  0.025:0.001  or  25:1.     Summar- 
izing: One  horsepower  in  the  stamp-mill  reduces  64  tons  per  month 
at  a  ratio  of  100:1,  and  in  the  tube-mill  36  tons,  at  25:1     These 
figures  are,  for  several  reasons,  far  from  accurate,  but  they  serve 
to  show  in  a  sketchy  fashion  the  largely  increased  power  cost 
of   fine-grinding.     In   connection   with   the   recent   notes*   of   Mr. 
Butters  on  the  necessity  of  heavy  foundations  for  the  tube-mill, 
it   is  interesting  to   note  that   the   foundations   at   the   Standard 
are  piers  of  heavy  timbers,  tied  and  bolted  together  with  heavy 
angle  pieces  of  J  by  8  in.  flat  iron  and  carefully  bedded  on  mud- 
sills set  in  hardpan.     Mr.  Nutter  tells  me  that  after  nearly  a  year's 
use,  these  were  tested  with  a  transit  and  found  unmoved.     As  a 
final  comment  upon  the  tube-mill,  it  can  be  said  that  it  has  proved 
itself  a  highly  efficient  fine-grinding  machine,  but  that  when  the 
whole  plant  depends  upon  a  single  unit,  as  in  this  case,  any  accident 
to  it  shuts  down  the  whole  plant.     This  virtually  demands    the 
duplicating  of  the  entire  tube-mill  equipment — for  a  small  plant, 
-a  heavy  extra  capital    expense.     This    led  to    experiment  with  a 
modified  pan  for  fine-grinding.     It  was  found  that  a  single  five- 
foot  pan  had  a  capacity  of  about  five  tons  per  24  hr.  and  consumed 

*MINING  AND  SCIENTIFIC  PRESS,  May  26,  1906 


THE  MOORE  FILTER— I.  97 

10  h. p.  or  from  eight  to  nine  pans  were  required  to  handle  the  coarse 
product  of  20  stamps,  at  a  marked  increase  of  power-cost.  No 
determination  was  made  of  wear  of  metal,  but  judging  from 
experience  with  grinding  concentrate  it  would  be  high,  and  prob- 
ably the  labor  of  attending  to  a  battery  of  pans  would  be  large. 
Altogether  for  a  small  plant,  so  far  as  this  experience  goes,  three 
smaller  tube-mills,  any  two  of  which  could  do  the  whole  work, 
would  be  preferable  to  pans,  and  probably  cheaper  in  installation 
than  two  large  units. 

The  per  cent  of  solids  has  been  increased  in  the  tube-mill 
discharge  to  25%,  or  perhaps  higher,  by  the  addition  of  material 
from  the  ponds.  The  settling  vats,  of  which  there  are  nine,  aggre- 
gate a  capacity  of  21,000  cu.  ft.;  they  are  flat-bottomed  wooden 
vats  in  two  sizes  of  70  and  80  tons  solution  capacity,  representing 
2,200  and  2,550  cu.  ft.  respectively.  On  the  basis  of  inflow  of 
400  cu.  ft.  per  hour,  the  one  size  fills  in  5.5  hr.  and  the  other  in 
6.4  hr.  While  filling  they  are  agitated,  then  allowed  to  settle  28 
hr.  and  slowly  decanted  down  to  the  upper  surface  of  the  slime. 
This  occupies  eight  hours  and  two  more  hours  are  taken  to  mix 
and  pump  out  the  sludge,  a  total  of  about  43  hr.  Forty-two 
per  cent  of  the  solution  is  recovered  by  decantation.  It  passes 
to  an  additional  clarifying  tank  and  then  to  the  gold  tanks.  The 
remaining  pulp  carries  from  34  to  40%  solids.  Returning  to 
the  mechanical  details  of  the  settling  room :  The  agitators  are  drags, 
actuated  by  a  vertical  shaft,  driven  by  overhead  crown  gear- 
ing, but  stepped  on  a  steel  button,  running  in  quicksilver, 
on  the  floor  of  the  tank.  Above  any  level  at  which  the  heavier 
pulp  can  collect,  an  8  by  8  in.  crose-arm  is  secured  to  the  shaft 
and  from  this  the  drags  hang  by  links  or  short  chains.  The  drags 
are  short  lengths  of  30-1  b.  T  rail;  the  speed  of  seven -or  eight 
r.p.m.  is  ample  and  the  power  consumption  is  low.  This  drag  type 
of  agitator  is  essential,  as  otherwise  the  slime  packing  around 
the  blades  would  stall  the  driving  gear.  After  decantation,  the 
pulp  is  made  homogeneous  by  stirring  with  the  drags  and  then 
transferred  to  the  storage  or  treatment  vats  by  centrifugal  pump 
or  air-lift,  both  devices  being  used.  For  decantation  there  are 
hinged  pipes  that  are  lowered  into  the  vat,  after  the  requisite 
clearness  is  attained  and  that  can  be  kept  near  the  surface  so  as 
to  draw  off  the  least  turbid  solution.  These  discharge  through 
the  sides  of  the  vat  a  short  distance  above  the  bottom.  The 
sludge  is  drawn  off  through  pipes  in  the  bottom. 


CYANIDE  PRACTICE  WITH  THE  MOORE 
FILTER— II 

BY  R.  OILMAN  BROWN 

(September  8,  1S06) 

So  little  has  been  published  concerning  the  Moore  process 
that  no  excuse  is  needed  for  explaining  it,  with  as  much  minuteness 
as  is  possible  in  the  absence  of  notes  and  working  drawings. 

The  points  in  common  between  the  Moore  and  the  Cassel- 
Butters  process  are:  The  nitration  by  vacuum,  with  the  resulting 
adhesion  of  the  cake  to  the  outside  of  the  filter;  and  the  general 
type  of  filter,  which  allows  a  great  area  in  compact  and  cheap  form. 
It  seems  to  me  that  the  point  of  adhesion  of  slime  to  the  filter, 
making  possible  its  removal  from  the  remaining  pulp,  is  the  real 
point  of  difference  between  these  and  other  slime  methods.  Others 
in  plenty  have  filtered  by  suction,  others  have  used  parallel  closely 
spaced  units  to  secure  maximum  area  in  minimum  volume,  but  so 
far  as  I  know  the  adhesion  of  a  cake  to  the  outside  of  a  filter  and 
its  removal  by  this  means  from  the  unfiltered  pulp  is  the  essential 
novelty  with  which  the  Moore  process  should  justly  be  credited, 
in  practice,  at  least.  The  essential  difference  between  the  Moore 
and  the  Cassel-Butters  method  may  be  considered  an  inversion 
of  the  Mountain-Mahomet  theorem;  Moore  transfers  the  filters, 
with  their  load  of  slime,  by  means  of  a  traveling  crane  from  the  pulp 
to  the  wash-water  tank  and  then  to  the  discharge  hopper,  while 
the  Cassel-Butters  plan  removss  the  pulp  from  the  filters  by  pumps 
of  large  volume,  substitutes  wash-water  and  then  discharges, 
the  operation  being  conducted  in  the  same  vat. 

In  the  Standard  Co.'s  plant  the  filters  are  of  canvas  of  medium 
weight,  5  ft.  wide  and  16  ft.  long;  the  canvas  is  double,  sewed 
round  three  edges,  and  the  fourth  (long)  edge  is  bolted  between 
slips  of  Oregon  fir  (QQ,  Fig.  3)  1J  by  6  in.  in  cross-section.  In  the 
bottom  edge  of  each  filter  or  'plate'  is  a  f-in.  channel-iron  (RR) 
that  serves  as  a  launder  for  the  in-filtered  solution.  The  filters 
are  stitched  through  both  sides  vertically  at  four-inch  distances 
and  in  the  compartments  thus  formed  J  by  1  in.  strips  are  inserted 
to  allow  circulation.  Within  each  filter  a  1-in.  vertical  suction- 
pipe,  flattened  at  the  end  so  as  to  dip  into  the  channel-iron  launder, 


bo 
£ 


i 

JIT 

f 

100  RECENT  CYANIDE  PRACTICE. 

reaches  to  the  bottom  from  the  outside.  The  outer  end  of  this 
is  connected  by  a  short  length  of  suction-hose  to  a  three-inch 
manifold,  through  which  the  suction  is  applied.  The  details  of 
this  will  be  better  understood  by  reference  to  Fig.  3:  A  is  one 
of  the  vertical  suction-pipes,  B  the  manifold  in  end-view  and  A1 
and  Bl  the  plenum-pipes  and  manifolds.  In  the  Standard  Co.'s 
plant  there  are  49  of  these  'plates'  hung  from  a  frame  of  steel 
I-beams  (EEE,  FFF),  the  distance  between  centres  being  four 
inches.  This  constitutes  the  'basket,'  approximately  16  ft.  square. 
On  the  top  of  this  rests  a  suction-pump  (C)  12  by  12  in.  driven 
by  a  10-h.p.  D.  C.  motor  (D),  which  derives  its  current  from  the 
crane  overhead.  With  a  vacuum  of  20  in.  the  motor  consumes 
3  h.p.  of  current,  but  in  the  early  part  of  the  cycle  when  filtering 
is  fast,  there  is  a  heavy  rise  in  power  at  the  end  of  the  stroke 
due  to  expelling  solution  from  the  slender  clearance  space.  To 
equalize  this  the  pumps  have  heavy  fly-wheels.  Clearly  this  bas- 
ket arrangement  lends  itself  to  great  area  of  filtering  surface, 
there  being  7,840  sq.  ft.  concentrated  in  each  unit.  The  basket 
is  hung  by  four  endless  one-inch  pitch-chains  to  the  overhead 
crane  and  is  raised  or  lowered  by  a  10-h.p.  motor  (G)  through  the 
medium  of  balanced  worm  gearing  and  differential -chain-wheels. 
The  driving  pulley  on  the  motor  is  indicated  at  H  and  the  driven 
pulley  at  /,  on  the  worm  shaft  /;  KK  are  the  worm-wheels,  keyed 
on  the  shafts  of  the  pocket-wheels  MM.  These  worm-gears  are 
right  and  left  thread.  The  worms  bear  on  collars  on  the  ends  of 
the  worm-shaft  and  the  direction  of  rotation  is  such  that,  raising 
the  load,  puts  shaft  /  in  tension;  at  the  same  time  the  worms 
being  right  and  left,  there  is  practically  no  end-thrust  on  the  bear- 
ings. The  pocket-wheels  are  of  six  and  seven  pockets  respectively. 
The  crane-motor  and  pump-motor  get  current  from  the  trolley- 
wires  NN  through  the  forks  and  wheels  OO;  P  is  the  insulated 
rest  onto  which  the  trolley-wire  drops,  when  not  held  up  by  the 
wheel  O.  The  crane-motor  is  operated  through  the  starting- 
box  T,  which  is  controlled  from  the  tank-floor  by  the  cords  U. 
The  total  maximum  load  of  the  full  basket  on  the  crane  is  35  tons 
and  this  is  raised  about  seven  feet  in  five  minutes.  This  represents 
about  3  h.p.  The  motor  consumes  8.4  h.p.  of  current,  so  that  the 
loss,  even  with  the  balancing  of  the  worms,  is  heavy.  Still,  as  the 
hoist  is  in  operation  not  above  one  hour  per  day,  this  is  negligi- 
ble. Notwithstanding  the  differential  gearing  was  furnished  by 


THE  MOORE  FILTER— II. 


101 


JS 


specialists,  it  gave  trouble  at  first,  largely 
because  the  pockets  in  the  wheels  were  not  deep 
enough  or  well  fitted  to  the  chain.  Even  now 
when  this  has  been  overcome,  guide-wheels  that 
were  devised  to  make  the  chain  grip  the  pockets 
better  are  retained  as  a  measure  of  precaution. 
Probably  any  future  design  should  have  wheels 
with  twice  the  number  of  pockets.  The  general 
construction  of  the  crane  is  clearly  indicated  by 
Fig.  3  and  the  photographs,  and  needs  no 
explanation.  The  pocket-wheels  are  placed  at 
quarter-span  points  of  the  large  I-beams,  and  all 
stress  calculations  were  for  a  factor  of  safety  of 
five.  The  supporting  track  is  of  60-lb.  T-rail 
and  rests  on  heavy  12  by  18  in.  longitudinal  sills, 
the  caps  of  the  supporting  sets.  To  prevent 
spreading  of  track,  the  sets  are  framed  back  to 
the  main  posts  of  the  building.  All  of  this  con- 
struction could  well  be  of  structural  steel  where 
transportation  cost  is  not  prohibitive.  The 
traversing  device  for  the  crane  is  a  f-in.  plough- 
steel  wire-cable,  run  over  three  and  four-grooved 
sheaves,  after  the  manner  of  the  Koepe  hoist, 
the  main  sheave  being  driven  by  a  worm-gear 
from  the  main-line  shaft.  A  grip  on  the  crane 
engages  the  cable  and  the  gear  is  started, 
stopped,  and  reversed  by  a  belt-shifter  through 
the  medium  of  levers  conveniently  placed  for 
operation  by  the  basketman.  The  tail-sheave 
is  on  a  carriage  and  adjustable  to  take  up  stretch 
of  the  cable.  The  rate  of  travel  is  five  feet  per 
minute.  Fig.  4  shows  the  general  plan  of  the 
filtering-vats  and  the  discharge-hoppers.  The 
filtering-vats  (which,  along  with  the  others, 
belonged  to  the  former  sand-plant)  are  round, 
flat-bottomed  vats  24  ft.  diam.  by  7  ft.  deep. 
They  have  four-armed  agitators  (Fig.  3)  running 
at  Tr.p.m.  close  to  the  bottom.The  shaft  to  which 
these  are  attached  is  driven  by  crown-gearing 
below  the  tank.  A  special  stuffing-box  devised 


102 


RECENT  CYANIDE  PRACTICE. 


to  keep  the  sand  out  of  the  bearing  has  proved  satisfactory 
but  could  be  improved  upon.  In  addition  to  the  agitators,  each 
filtering  vat  is  fitted  with  two  six-inch  air-lifts  discharging  onto 
two  distributing  launders  on  the  tops  of  the  baskets.  These  are  run 
intermittently  during  the  accretion  period  and  serve  to  bring  the 
coarser  particles  to  the  surface,  whence,  as  they  slowly  settle, 
they  are  caught  by  the  suction  currents  and  deposited  on  the 
filter  with  the  slime. 


Fig. 


Moore  Filter,  with  Cake. 


The  action  of  the  filtering  process  is  as  follows:  The  basket 
is  lowered  into  the  vat  full  of  pulp,  until  the  tops  of  the  slats  are 
submerged,  and  the  suction  pump  is  started.  The  first  solution 
coming  through  muddy  is  turned  back  into  the  vat.  It  soon  clears, 
however,  unless  a  filter  leaks.  Should  there  be  a  leak,  the  identity 
of  the  faulty  filter  is  quickly  established  by  an  inspection  of  the 
glass  nipples  connecting  each  individual  'plate'  with  the  manifold, 
and  that  plate  is  cut  out  by  closing  the  proper  service  cocks  in  the 


THE  MOORE  FILTER— II. 


103 


manifolds.  Suction  is  continued  with  intermittent  agitation  un- 
til a  sufficient  coat  is  obtained,  which  in  this  case  averages  }  in.; 
then  the  basket  is  raised,  the  suction-pump  still  running,  and  trav- 
ersed, with  its  load  of  slime  adhering,  over  the  wash- water  tank 
and  lowered  therein.  Here  suction  is  continued  with  frequent 
titration  of  the  filtrate  toward  the  end,  till  the  solution  has  fallen 
to  the  predetermined  minimum  net  strength  of  cyanide.  The 
displacement  is  good,  about  0.7  ton  wash-water  being  needed  per 


Fig.     6.     End  View  of  Moore  Filter-Basket. 

ton  of  dry  slime;  the  cake  in  this  condition  carries  about  40% 
moisture,  so  that  every  ton  of  slime  is  accompanied  by  0.67  ton 
solution.  The  limiting  net  cyanide  content  of  the  filtrate  is  the 
difference  between  that  in  the  wash-water,  which  always  contains  a 
little  that  has  been  soaked  off  from  previous  charges,  and  that  of 
the  nitrate.  This  is  in  the  neighborhood  of  0.15  Ib.  per  ton  or 
0.0075  per  cent. 


104  RECENT  CYANIDE  PRACTICE. 

After  washing,  the  basket  is  raised  again  and  run  over  the 
discharge-hopper;  the  suction  is  continued  till  excess  moisture 
is  removed  and  then  an  air-pressure  of  35  Ib.  is  turned  on,  in 
successive  blasts  of  a  few  seconds  each.  This  causes  the  cakes  of 
slime  to  drop  off,  the  discharge  averaging  about  85%  of  com- 
pleteness. Every  alternate  day  the  niters  are  cleansed  by  sub- 
stituting water,  under  20-lb.  pressure,  for  air.  On  each  basket 
there  are  two  special  air-manifolds  connecting  with  the  inside 
of  each  filter,  at  points  four  feet  from  the  ends.  Probably  these 
could  be  omitted,  and  the  vacuum  manifold  be  used  for  the  plenum 
as  well.  The  discharged  sludge  averages  68%  solids  and  is 
sluiced  from  the  hoppers  into  the  waste-flume,  about  a  ton 
of  water  being  used  for  each  ton  of  slime.  The  grade  of 
flume  for  this  class  of  material  is  9/16  in.  per  ft.  The  time  con- 
sumed in  a  single  cycle  depends  primarily  upon  the  thickness 
of  the  pulp;  as  an  instance,  a  pulp  of  20%  solids  will  scarcely  build 
up  a  one-half  inch  coating  in  10  hr.,  while  pulp  of  40%  solids 
will  give  an  inch  coating  in  two  to  three  hours.  The  average 
thickness  for  last  year  was  0.74  in.  and  the  maximum  for  any  one 
month  1.14  in.  The  time  of  the  accretion  period  is  about  three 
and  one-half  hours;  washing  and  discharging  take  the  same,  making 
about  three  full  cycles  in  24  hr.  with  time  for  emergency  matters. 
This  is  considerably  longer  than  is  the  experience  elsewhere  and 
must  be  attributed  to  the  large  proportion  of  clay  in  the  material. 
During  one  month,  when  clay  was  notably  less,  the  average  fell 
to  2.35  hr.  for  accretion  and  2.9  hr.  for  washing  and  discharge. 
The  average  load  handled  in  each  cycle  is  close  to  18  tons  of  dry 
slime,  so  that  the  two  units  in  this  plant  have  an  average  capacity 
of  108  tons  per  diem.  This  has  not  been  obtained  in  practice 
over  any  extended  period,  but  the  limiting  factor  has  not  been 
the  filtering,  so  that  the  monthly  capacity  of  the  plant  has  been 
conservatively  placed  at  3,000  tons  per  month.  Fifty-eight  per 
cent  of  the  total  solution  recovered  from  the  plant  has  come  through 
the  filters.  Beyond  this  point  the  process  is  the  same  as  in  any 
cyanide  plant  except  that  the  sump  solutions,  after  being  standard- 
ized in  storage -tanks,  are  returned  by  a  three-plunger  pump  to 
the  mill. 

Taking  up  some  of  the  details  not  yet  touched  upon  the  follow- 
ing is  to  be  noted:  The  question  of  the  wear  of  the  filters  is  an  im- 
portant one.  An  extreme  life  of  10  months  has  been  noted  in 


THE  MOORE  FILTER— II.  105 

some  cases,  but,  if  badly  made  or  carelessly  handled,  they  require 
constant  attention,  repairs,  and  renewals;  half  a  cycle  per  day 
can  easily  be  lost  in  this  way.  Six  months  can  be  taken  as  a  fair 
average  life ;  this,  at  a  monthly  tonnage  of  1,500  per  basket,  makes 
the  cost  5c.  per  ton.  In  other  plants  where  smaller  filters  are 
used,  the  canvas  is  stretched  on  an  internal  frame  of  pipe  and  so 
kept  taut,  the  pipe  at  the  same  time,  serving  for  suction  and 
discharge-pressure.  In  the  Standard  plant  no  trouble  has  been 
experienced  from  letting  the  filters  take  their  natural  hang,  and 
when  the  plant  was  being  designed,  the  stretching  of  the  canvas 
over  a  frame  did  not  appeal  to  us,  both  because  of  added  expense -of 
construction  and  of  shorter  life  of  the  canvas,  which  wTould  be 
under  greater  tension  when  the  'plates'  distend  under  air-pressure 
and  become  distorted.  Whether  the  latter  is  a  valid  objection, 
only  unbiased  comparative  work  can  tell.  The  individual  'plates' 
are  spaced  one  from  the  other  by  light  wooden  rods  to  which  their 
edges  are  attached  by  twine.  There  are  four  of  these,  spacing 
the  ends  of  the  'plates'  at  middle  and  lower  corners.  As  a  certain 
amount  of  slime  gets  through  the  filter  at  times  (when  a  leak  de- 
velops when  the  basket  man  is  not  at  hand)  the  solution  passes 
from  the  pump  through  a  launder  first  to  a  clarifying-tank  from 
which  it  is  decanted  to  the  gold-tanks.  An  addition,  recently 
installed  as  an  improvement  on  this,  is  a  permanent  set  of  'plates' 
in  the  clarifying  vat,  through  which  the  solution  is  drawn.  This 
device  is  used  elsewhere  with  success. 

From  tailing  averaging  about  $8  per  ton  the  average  return 
has  been  83%  of  the  gold  and  silver,  the  gold  alone  being  close 
to  90%.  Higher  results  have  been  at  times  attained,  and  the 
indications  are  that  the  average  for  the  present  year  will  tend 
to  approach  these  figures.  The  total  extraction  from  the  ore 
is  as  given  herewith;  the  third  column  gives  the  results  for  a  $20 
ore,  this  being  about  the  average  for  the  mine: 

Per  cent  Per  cent 

0  of  product.  of  crude  ore. 

Recovery  in  the  mill 54  54.0 

Recovery  in  the  slime  plant 83 

Total  recovery 92  . 2  $18 . 44 

Comparing  this  with  the  old  method  by  percolation,  we  have 
the  following: 


106  RECENT  CYANIDE  PRACTICE. 

Recovery  in  the  mill 64  64.0  $12.80 

Recovery  in  the  cyanide  plant   70  25.2  5.04 

Total  recovery 89 . 2  $17 . 84 

This  gain  of  3%  or  60  cents  per  ton  is  small  and  hardly  more 
than  enough  to  cover  the  extra  cost  which  on  the  basis  of  work 
during  last  fall  is  22c.,  so  that  it  does  not  furnish  a  strong  argument 
for  fine  grinding  in  cases  where  the  whole  product  is  amenable  to 
percolation.  But  so  far  as  this  ore  goes,  and  many  like  it,  the 
comparison  is  by  no  means  fair.  Under  the  former  method  of 
treatment  30%  of  the  tailing  was  left  in  the  ponds,  being  unfit 
for  any  but  slime  methods.  The  revised  comparison  then  would 

be  as  follows : 

Percentage  Percentage 

of  of 

Old  method.                                                 product.  crude  ore.  Value. 

Recovered  in  the  mill : . 64  64.0  $12  .80 

Discharged  from  the  mill 36  36.0  7 . 20 

Left  in  the  ponds 30  10.8  2.16 

Going  to  cyanide  plant 70  25.2  5  . 04 

Saved  in  cyanide  plant 70  17.6  3  . 52 

Total  saving 81.6  $16 . 32 

This  shows  a  gain  of  $2.12  per  ton,  ignoring  any  difference 
in  cost.  In  our  work  last  fall  this  came  to  $0.22  increase,  so  that 
the  net  gain  is  $1.90  per  ton.  Roughly,  the  plant  cost  $60,000, 
though  it  could  probably  be  duplicated  for  one-fourth  less,  so  that 
on  the  basis  of  the  tonnage  of  20,000  per  year  the  gain  represents 
63%  return  per  annum  on  the  actual  cost  of  the  plant,  fully  justify- 
ing the  investment.  In  addition  to  this  gain  is  the  ability  to 
treat  some  40,000  tons  of  accumulated  slime,  which  has  thus  be- 
come an  asset.  The  above  comparison  is  on  the  figures  of  cost 
actually  attained;  using  the  cost  of  $2,  estimated  for  the  future, 
the  gain  would  be  $2.37  per  ton. 

The  following  table  gives  the  segregation  of  cost  for  the  various 
departments : 

General    expense,    including    superintendence,   *vatchman,    assays, 

insurance,  taxes,  chemicals,  supplies,  etc $1 . 202 

Re-grinding ' 0 .  572 

Moore  process 0  .  31  -1 

Zinc  room. .  0.261 


Total  in  slime  plant $2 . 349 

Ponds,  collecting  and  handling,  with  team 0. 120 

Grand  total  . .  .    $2 . 469 


THE   MOORE  FILTER— II.  107 

By  the  disc-harrow  percolation  method,  formerly  followed, 
the  cost  was  $2.25.  This  figure  of  $2.47  is  for  a  restricted  tonnage, 
and  careful  estimate  on  a  basis  of  3,000  tons  per  month  brings  the 
cost  down  to  $2.  Future  work  should  improve  even  on  this. 
Mention  has  been  made  of  the  accumulated  tailing.  This  material 
has  been  made  available  for  immediate  treatment  by  the  provision 
of  a  stock-bin  outside  the  grinding-house.  It  is  connected  on  the 
one  side  with  the  ponds  by  an  inclined  track  and  a  stationary 
hauling  system  and  on  the  other  with  the  tube-mill  by  a  steep 
launder,  into  which  the  tailing  is  fed  from  the  bin,  mechanically. 
In  the  case  of  ore  of  this  kind  with  qualities  of  very  slow  settling, 
the  addition  of  dry  material  is  a  decided  advantage  to  the  plant, 
as  it  increases  the  percentage  of  solids  and  lessens  the  time  of 
settling.  It  is  probable  that  this  outside  stuff,  not  having  par- 
ticipated in  the  violent  agitation  with  cyanide  solution  accom- 
plished in  the  mortars,  and  moreover  only  coming  into  contact  with 
the  solution  that  reaches  the  tube-mill  already  weakened  from  its 
original  strength  of  two  pounds  by  the  'cyanicides'  in  the  ore, 
does  not  yield  as  highly,  and  so  cuts  down  the  average  extraction 
pro  rata. 

To  the  experienced  cyanide  man  a  question  naturally  presents 
itself  as  to  the  accumulation  of  weak  solution.  The  addition  to 
the  bulk  of  solution  comes  from  moisture  in  the  ore  and  from  the 
wash-water,  the  losses  from  evaporation  and  leakage  and  from 
the  discharged  tailing.  On  the  basis  of  the  dry  ton,  the  additions 
are  0.09  ton  +  0.7=  0.79,  while  the  determinable  losses  are  0.47 
ton.  This  indicates  an  increase  that  is  not  found  in  practice. 
But  if  it  were,  the  extreme  weakness  of  the  solution  would  make 
such  a  gain  not  of  first  moment.  Just  how  the  difference  is  to  be 
accounted  for,  is  not  clear,  but  it  is  due  in  part  at  least  to  the  diffi- 
culty of  correctly  determining  the  moisture  in  the  discharge. 

For  years  the  concentrate  has  been  treated  in  a  pan,  with 
a  lye  and  bluestone  charge,  giving  results  that  were  only  satis- 
factory because  no  way  had  appeared  of  bettering  them.  Soon 
after  the  slime-plant  had  been  put  in  operation,  the  experiment 
was  tried  of  treating  the  concentrate  with  strong  cyanide  solution, 
and  with  such  good  results  that  the  method  completely  supplanted 
the  old.  The  details  are  as  follows:  The  concentrate  consists 
largely  of  iron  oxides  with  a  little  pyrite.  This  is  charged  in  one- 
ton  lots  into  an  ordinary  five-foot  silver  pan,  25  Ib.  lime  is  added 


108  RECENT  CYANIDE  PRACTICE. 

and  enough  water  to  bring  the  pulp  to  about  45%  solids,  giving  the 
consistence  of  thick  cream.  The  charge  is  ground  for  48  hr. 
and  then  cyanide  is  introduced,  to  bring  the  solution  up  to  a 
strength  of  24  Ib.  per  ton.  Grinding  is  continued  with  the  addi- 
tion of  lime  and  cyanide  at  intervals,  the  one  to  insure  alkalinity 
and  the  other  to  keep  up  the  strength  to  the  original.  After  about 
72  hr.  it  passes  to  the  settler  for  24  hr.  further  agitation  and  finally 
is  diluted  with  mill  solution  and  turned  into  the  slime-plant  flume. 
Toward  the  end  of  the  operation,  samples  of  the  pulp  are  taken 
at  intervals,  washed  clean  of  solution  and  assayed,  as  a  check 
upon  the  extraction. 

An  interesting  feature  is  that  during  the  grinding  with  lime, 
an  oxidizing  action — a  sort  of  wet  roast — appears  to  take  place, 
the  pulp  changing  from  a  dirty  green  to  a  brownish  red.  The 
results  of  this  work  for  some  30  tons — one  half  the  year's  product— 
with  an  assay-value  of  over  $150  per  ton,  are:  Extraction  of  gold, 
96.8%;  of  silver,  84.1%;  total,  94.9%;  the  cost  is  $7.91  per  ton. 
The  consumption  of  cyanide  is  18  to  20  Ib.  per  ton.  An  excellent 
comparison  of  the  new  and  the  old  method  is  obtained  by  con- 
sidering the  work  of  the  first  half  of  the  year,  which  was  by  pan 
amalgamation:  Extraction  of  gold,  87.1%;  of  silver,  74.9%;  total, 
84.4%  ;  cost,  $13.38  per  ton.  On  $150  concentrate  the  gain  per  ton 
amounts  to  $15.75  in  extraction  and  $5.47  in  cost,  a  total  of  $21.22. 

To  the  advocate  of  fine  grinding  the  results  I  have  given 
may  appeal  with  too  great  force.  Stamping,  if  followed  at  all, 
must  almost  of  necessity  be  in  solution,  and  the  low  cyanide  con- 
tent demanded  by  more  than  one  factor  is  apt  to  give  low  results 
as  regards  -the  silver.  In  an  ore  which,  by  reason  of  absence  of 
coarse  gold,  will  yield  creditably  to  cyanide  alone,  amalgamation 
can  be  dispensed  with  and  probably  less  solution  used.  But  it 
is  doubtful  if  even  then  a  solution  strong  enough  for  good  silver 
extraction  could  be  used  without  excessive  loss.  Certainly, 
however,  in  ore  of  the  Standard  type  fine  grinding  gives  higher 
results  for  the  same  cyanide  strength  and  the  same  extraction 
for  a  lower  strength.  Between  the  two  there  is  intermediate 
strength  that  gives  the  maximum  commercial  result,  and  in  all 
tests  with  fine  grinding  the  aim  must  be  to  determine  this  point. 
As  a  comparison  between  the  general  Moore-Cassel-Butters  method 
and  filter  pressing,  it  seems  that  the  former  has  great  inherent 
advantages  in  cheapness  of  installation  and  operation,  and  growing 


THE   MOORE   FILTER— II.  109 

familiarity  with  the  details  should  make  this  increasingly  evident. 
In  comparison  with  decantation,  apart  from  the  fact  that  for  some 
ore  decantation  is  entirely  unsuited,  it  does  away  with  the  enormous 
bulk  of  solutions,  from  the  repeated  washings.  In  fine,  it  is  believed 
that  once  metallurgists  become  better  informed  on  the  principles 
of  the  system,  it  will  be  found  worthy  of  more  consideration  than 
heretofore. 


TUBE-MILLING  IN  KOREA 

(September  22,  1906) 

The  Editor: 

Sir — We  are  at  present  experimenting  on  a  practical  scale 
with  re-grinding  our  concentrate  in  a  tube-mill  with  cyanide 
solution.  It  occurred  to  me  some  months  ago  that  cyanide  solution 
could  be  used  just  as  well  as  water,  when  reducing  our  concentrate 
to  slime,  and  incidentally  some  of  the  gold  could  be  extracted  while 


Fig.     7.     Experimental  Cyanide  Plant. 

grinding.     In  other  words,  the  tube-mill  could  be  used  as  a  grinder 
and  agitator  combined. 

This  company  (Oriental  Con.  Mining  Co.)  has  constructed  an 
experimental  plant  consisting  of  one  tube-mill  (2J  by  12J  ft.), 
two  mechanical  agitators  with  plow  shoes  (8  by  6  ft.  diam.),  three 
filter  and  settling-boxes  (4  by  5  by  5  ft.),  48  separate-compartment 
zinc-boxes,  two  sumps,  and  one  stock-solution  vat.  An  electric 


TUBE-MILLING  IN  KOREA. 


Ill 


motor    furnishes    the  necessary  power.     The  tube-mill  was   con- 
structed in  this  company's  shops. 

The  method  is  a  continuous  one;  the  concentrate  is  put  into 
the  hopper  with  cyanide  solution  and  upon  passing  through  the 
tube-mill  is  nearly  all  ground  to  slime  and  a  good  percentage  of 
the  gold  is  extracted.  At  the  end  of  the  mill  is  a  spitzkasten  (3  in. 
wide  by  1^  ft.  long  by  1J  ft.  deep)  supplied  with  clear  water  from 
the  bottom.  What  discharges  from  the  bottom  of  the  spitz- 
kasten is  coarse  concentrate  and  clear  water,  that  passing  over  the 
spitzkasten  is  the  cyanide  solution  and  slime.  The  coarse  con- 


Fig.  8.     Another  View  of  the  Same. 

centrate  that  may  escape  from  the  tube-mill  is  caught  in  the  settling- 
boxes  and  again  re-ground,  while  the  overflow  contains  very  little 
value  (tests  0.005  to  0.01%  KCN  and  assays  six  cents  per  ton). 
We  cannot  arrange  to  run  this  overflow  or  waste-water  solution 
through  a  separate  line  of  zinc-boxes.  In  this  small  plant  the  value 
of  this  waste  solution  will  not  amount  to  more  than  $2  to  $3  in  24 
hours.  The  slime  concentrate  and  cyanide  solution  pass  on  to  an 
agitator  which  has  been  set  in  motion  (13  rev.  per  min.)  and  the 
muller  lowered.  Here  the  product  is  agitated  for  about  15  hr., 
the  muller  is  then  raised  two  feet,  the  agitator  stopped  and  the  con- 


112 


RECENT  CYANIDE  PRACTICE. 


centrate  allowed  to  settle.  It  takes  about  one  hour  to  settle  clear; 
'by  the  addition  of  some  milk-of-lime  it  could  be  made  to  settle 
in  half  an  hour.  I  prefer  to  use  as  little  lime  as  possible  because 
the  strong  alkaline  solution  consumes  a  large  amount  of  zinc. 
The  clear  cyanide  solution  is  decanted  by  a  float  siphon  into  filter- 
boxes  and  from  there  it  is  run  through  the  zinc-boxes  and  the  gold 
precipitated.  Next,  the  strong  precipitated  cyanide  solution 


Fig.  9.     Tube-Mill  and  Experimental  Cyanide  Plant. 

from  the  sump  is  pumped  up  to  the  agitator  as  a  wash  to  partly 
remove  the  gold  remaining  within  the  settled  concentrate.  The 
muller  is  allowed  to  work  down  on  the  charge  and  agitate  for  a  few 
minutes,  then  settled  and  decanted.  Following  this  come  two 
successive  weak  cyanide  washes  to  remove  cyanide  and  gold,  and 
finally  a  water-wash  which  is  run  through  a  row  of  zinc-boxes 
to  waste.  Now  the  charge  of  about  five  tons  of  clean  concentrate 
is  ready  to  be  discharged  into  the  creek.  A  little  water  is  added, 


TUBE-MILLING  IN  KOREA.  113 

the  muller  set  in  motion  and  lowered,  the  discharge-hole  opened, 
and  now  the  agitator  will  discharge  itself  readily  and  prepare  for 
a  new  charge.  The  total  treatment  takes  24  hours,  both  agitation 
and  decantation  being  done  in  the  agitators. 

By  feeding  the  concentrate  and  cyanide  solution  with  a  con- 
sistence of  one  to  one  through  the  tube-mill,  we  are  able  to  get 
the  finest  grinding  and  the  best  results.  The  agitators  will  only 
have  to  be  filled  once  to  contain  a  full  charge.  While  one  agitator 
is  being  filled,  the  other  is  decanting  and  getting  ready  to  be  dis- 
charged. At  the  head  of  the  launder  (leading  from  mill  to  agitator) 
a  pipe  was  run  to  the  stock  cyanide  vat  above,  so  that  we  can  add 
enough  solution  to  keep  the  launder  clear.  With  clean  concen- 
trate it  is  necessary  to  have  a  steep  grade. 

The  strong  cyanide  solution  (0.43%)  is  used  in  the  tube- 
mill  and  agitators,  while  the  weak  one — employed  for  washes — 
tests  0.1%.  No  cyanide  is  added  to  the  weak  soluton.  Lime  is 
added  (about  two  pounds  per  ton)  with  the  concentrate  as  it  is 
fed  into  the  mill. 

|H  The  old  method  of  cyaniding  concentrate  here  is  by  mixing 
with  48%  sand  and  percolating  in  vats  from  20  to  30  days.  This 
method  gives  an  average  extraction  of  80  per  cent. 

The  extraction  obtained  at  present  with  the  tube-mill  and  agita- 
tors on  clean  concentrate  is  93%.  By  gradually  making  improve- 
ments we  may  possibly  better  these  results. 

A.  E.  DRUCKER. 

Chittabalbie,  Korea,  July  20,  1906. 


CYANIDE  PRACTICE  AT  EL  ORO— I 
BY  T.  A.  RICKARD 

(September  29,  1906) 

The  development  of  the  milling  practice  at  El  Oro  is  full 
of  interest.  In  1873  a  hacienda  de  beneficio,  or  reduction  plant, 
was  erected  to  crush  ore  and  treat  the  accumulated  tailing  from 
a  still  older  arrastre,  and  to  this  plant  further  addition  was  made 
in  1885.  The  mill  then  included  25  stamps  with  amalgamating 
tables.  .  In  1890  the  accumulation  of  tailing  made  by  the  stamps 
was  sold  to  a  man  from  Butte,  named  Albertson.  The  tailing 
he  handled  was  richer  than  the  ore  being  mined  today.  Never- 
theless, the  contract  for  the  treatment  of  it  was  cancelled  after 
the  purchaser  had  installed  four  amalgamating  pans  with  settlers 
and  had  started  to  ship  bullion.  This  was  under  the  regime  of 
General  Frisbie.  In  1894  a  Chilean  mill  was  brought  from  Chicago, 
to  grind  the  ore  after  it  passed  through  a  Comet  crusher.  The 
Chilean  mill  did  finer  grinding  than  the  stamps,  which  at  that 
time  were  also  preceded  by  crushers,  of  the  Blake  type.  The  mill 
in  turn  left  a  dump  which,  eventually,  as  methods  improved, 
it  became  profitable  to  re-treat.  Late  in  1894,  James  B.  Haggin 
bought  control.  In  the  following  year  the  old-mule  stable  was 
converted  into  a  cyanide  annex.  Redwood  tanks  with  4J-ft. 
staves  and  24  ft.  diameter  were  erected;  the  sump-tanks  were 
larger,  with  6-ft.  staves.  The  tailing  was  carried,  in  boxes  on  the 
backs  of  peones  and  in  hand-barrows,  to  the  vats.  Cyanide  solution 
was  first  introduced  by  upward  percolation  through  a  false  bottom, 
the  succeeding  water- washes  being  applied  from  above.  This 
.  was  followed  by  precipitation  on  zinc  shaving,  with  acid  treatment 
for  the  zinc  'shorts,'  the  bulk  of  the  precipitate  being  carefully 
washed  and  melted  forthwith.  The  bullion  thus  obtained  was 
of  extraordinary  fineness — 960  to  980 — without  the  use  of  any 
nitre  in  the  melting.  This  was  one  of  the  first  successful  cyanide 
plants  in  Mexico.  With  only  the  addition  of  the  small  cyanide 
plant  just  described,  the  mine  paid  $1,000,000  in  dividends  up  to 
May,  1898,  besides  meeting  the  cost  of  various  installations, 
including  part  of  the  100-stamp  mill  taken  over  by  the  English 
company,  which  now  controls  the  property. 


CYANIDE  PRACTICE  AT  EL  ORO—I.  115 

The  first  100-stamp  mill  was  designed  under  the  Haggin- 
Frisbie  regime  and  was  only  expected  to  crush  4,500  tons  per 
month  through  a  60-mesh  screen.  When  the  property  was  pur- 
chased by  the  Exploration  Co.  in  1898,  this  mill  was  too  near  com- 
pletion to  be  altered.  The  slime-plant  was  added  in  1900,  after 
the  present  company  had  been  formed.  W.  K.  Betty  had  con- 
ducted a  series  of  experiments  for  the  new  owners  and  double 
treatment  was  then  adopted  for  the  slime-plant ;  it  was  only  making 
the  best  of  conditions  as  they  were  found ;  hence  the  pile  of  stored 
tailing  now  about  to  be  re-treated. 

The  general  plan  of  treatment  was  as  follows:  From  the 
stamp-battery  the  pulp  passed  over  copper  plates  and  was  then 
divided,  by  spitzkasten,  into  'coarse  sand,'  'fine  sand'  and  'slime,' 
each  product  receiving  individual  treatment.  The  sand  under- 
went double  treatment,  in  South  African  style ;  it  was  first  cyanided 
in  collecting  vats  and  then  dropped  into  cars  which  removed  it  to 
the  treatment  vats.  The  slime  was  caught  in  a  settling  vat  and 
thence  went  to  the  treatment  house,  where  it  was  agitated  by  jets 
of  compressed  air.  After  treatment,  the  sand  was  dropped  into 
cars  underneath  the  vat,  while  the  slime  was  flushed  out  with 
water  in  the  ordinary  manner. 

In  the  meanwhile  the  capacity  of  the  mine  grew,  not  only 
by  reason  of  the  discovery  of  new  orebodies,  but  indirectly  through 
the  cheapening  of  operations,  so  that  further  enlargement  of  the 
mill  became  prudent.  In  1905  another,  and  the  last,  addition  to 
the  reduction  plant  was  made.  The  new  mill  of  100  stamps, 
with  its  up-to-date  cyanide  equipment,  differs  from  the  old  one 
in  five  respects: 

1.  Mechanical  handling  of  the  ore. 

2.  Heavier   stamps. 

3.  Re-grinding  in  tube-mills. 

4.  Mechanical  handling  of  sand  by  distributors,  excavators, 
and  belts. 

'         5.     Mechanical  agitation  of  slime  by  stirrers  and  centrifugal 
pumps. 

The  new  mill  contains  100  stamps,  each  weighing  1,180  lb., 
falling  102  times  per  minute,  with  a  6-in.  drop.  The  depth  of 
discharge  is  2J  to  3  in.  with  a  new  die,  and  3£  in.  when  the  die 
is  worn  out.  Woven  brass  wire-screens  of  35  mesh  are  used. 


CYANIDE  PRACTICE  AT  EL  ORO—I.  m 

The  accompanying  diagram*  (Fig.  10)  illustrates  the  process. 
From  the  stamps  the  crushed  ore  goes  to  a  system  of  cone-classifiers 
and  spitzkasten  which  separate  the  coarsest  sand  and  send  it 
to  the  tube-mills  for  re-grinding.  The  fine  sand  from  the  stamps 
combines  with  the  similar  product  from  the  tube-mills  and  is 
elevated  by  the  raff-wheel  to  the  sand-collecting  vats.  Any  slime 
which  may  have  escaped  complete  separation  and  accompanies 
the  sand,  overflows  from  these  vats  and  passes  to  the  slime-plant, 
joining  with  the  rest  of  this  product  that  has  been  eliminated 
from  the  sand  by  the  classifiers.  The  sand  is  distributed  by  a 
revolving  mechanism  of  the  Butters  &  Mein  type.  There  is  no 
chemical  treatment  in  the  sand-receiver,  the  idea  being  to  keep 
the  mill-water  free  from  cyanide  while  effecting  a  final  separation 
of  slime,  so  as  to  get  a  clean  product.  The  water  and  slime  are 
drawn  off  through  gates  or  slots  on  the  side  of  the  vats;  these  gates 
are  closed  by  a  roll  of  canvas  as  the  vats  fill.  The  sand,  when 
thus  finally  freed  from  the  last  trace  of  slime,  is  removed  by  a 
Blaisdell  excavator  which  drops  it  through  a  central  opening 
onto  a  Robins  belt-conveyor.  This  Blaisdell  excavator  is  like 
a  revolving  disc-harrow  and  it  has  proved  a  most  efficient  machine. 
It  uses  comparatively  little  power  and  works  smoothly.  The 
belt  conveyor  takes  the  sand  (containing  now  only  from  10 
to  11%  moisture)  to  the  treatment  vat,  which  is  fed  by  a  revolving 
distributor  operated  by  a  variable-speed  motor,  the  centrifugal 
force  being  so  regulated  as  to  throw  the  sand  to  the  sides  or  centre 
of  the  vat,  as  required.  The  charge  is  265  tons,  dry  weight. 
Ten  washes  of  alternately  medium  (0.1%)  and  strong  (0.2%) 
solution  are  introduced,  six  hours  apart.  This  treatment  is  fol- 
lowed by  no  less  than  thirty  'weak'  washes,  such  a  lengthy 
operation  being  specially  designed  to  extract  silver.  These  'weak' 
washes  are  four  to  six  hours  apart  and  contain  0.03%  KCy.  Each 
wash  is  equal  to  13  tons  of  solution.  After  treatment,  the  residue, 
again  using  the  Blaisdell  machine,  which  moves  on  rails,  is  dis- 
charged onto  a  conveyor  that  takes  it  to  the  dump.  Here  the 
distribution  of  tailing  is  regulated,  as  the  accumulation  grows, 
by  a  hinged  belt-conveyor  in  two  lengths,  the  last  one  being  swung 
round  according  to  the  contour  of  the  ground. 

*Borrowed  by  permission  from  'The  Grinding  of  Ore  by  Tube-Mills,  and  Cyaniding  at  El 
Oro,  Mexico,'  by  G.  Caetani  and  E.  Burt.  Trans.  A.  I.  M.  E.,  February,  1906.  This  is  a 
conscientious  and  most  valuable  paper,  giving  a  detailed  account  of  the  cyanide  practice  at 
El  Oro. 


118  RECENT  CYANIDE  PRACTICE. 

The  slime  goes  to  a  collecting  vat,  from  which  the  thick 
mud  is  drawn  off  at  the  bottom  and  thrown  into  one  of  the  treat- 
ment vats.  There  are  twelve  of  these,  each  34  ft.  diam.  and  12 
ft.  deep.  Here  it  is  agitated  with  a  proper  proportion  of  cyanide 
solution,  which  is  introduced  simultaneously.  The  apparatus 
for  stirring  consists  of  two  long  and  two  short  arms  made  of  oak 
bolted  to  a  steel  star.  The  oak  arms  are  solid ;  they  taper  outward 
from  a  cross-section  of  4  by  6  in.  to  4  by  4  in.  The  thick  end  is 
bolted  to  the  steel  star,  which  is  set  on  a  vertical  shaft.  When 
the  vat  is  charged,  lead  acetate  is  added  immediately.  Tests 
have  shown  that  a  beneficial  result  ensues  forthwith,  particularly 
as  regards  the  dissolution  of  the  silver. 

Lead  salts  when  added  in  excess  to  the  cyanide-solution, 
give  a  precipitate  of  basic  lead  cyanide,  but  when  present  in  small 
proportion  the  lead  remains  in  solution,  presumably  owing  to  the 
formation  of  an  alkaline  plumbite  (K2PbO2)  by  reaction  with  the 
caustic  alkali,  thus: 

PbAc2  +  4KOH  -  K2Pb02  +  2KAc  +  2H2O. 

Mercuric  chloride  is  sometimes  employed  for  the  same  purpose, 
producing  a  reaction  with  the  KCy  so  as  to  form  a  soluble  double 
cyanide,  thus: 

HgCl2  +  4KCy  -  K2HgCy4  +  2KC1. 

The  most  useful  effect  of  these  soluble  lead  and  mercury 
compounds  is  the  removal  in  the  form  of  insoluble  HgS  and  PbS, 
of  any  soluble  sulphides  that  would  otherwise  retard  the  solution 
of  gold  and  silver,  and  which  may  even  re-precipitate  silver  already 
dissolved : 

K2S  +  K2HgCy4  =  HgS  +  4KCy. 
K2S  +  K2PbO2  +  2H2O  =  PbS  +  4KOH. 

The  double  mercuric-potassium  cyanide  also  acts  as  a  solvent, 
attacking  gold  more  readily  than  simple  KCy;  and  this  aciton  is 
independent  of  the  presence  of  oxygen,  gold  replacing  mercury: 

K2HgCy4  +  Au  =-  K2AuCy4  +  Hg. 

Silver  is  similiarly  dissolved.  These  reactions  have  been 
amply  verified.  The  action  of  mercuric-potassium  cyanide  on  gold 
is  the  basis  of  patent  secured  by  Keith  and  Hood;  the  latter  also 
claims  the  use  of  lead  as  facilitating  the  solvent  effect  of  cyanide 


CYANIDE  PRACTICE  AT  EL  ORO—L  119 

solutions.  De  Wilde  has  a  patent  involving  addition  of  lead 
oxide  to  cyanide  solution.  These  compounds  also  influence 
precipitation  beneficially  if  they  remain  in  the  solution  up  to  the 
point  of  entering  the  zinc-box,  as  in  that  case  the  lead  and  mercury 
are  precipitated  on  the  zinc,  forming  zinc-lead  and  zinc-mercury 
couples  of  high  electro-motive  force.  In  this  precipitation  the 
zinc  simply  changes  places  with  the  mercury  or  lead,  aa  is  also  the 
case  when  zinc  shaving  is  dipped  in  lead-acetate  solution. 

The  charge  is  60  tons  (dry  weight)  of  slime;  this  is  mixed 
with  a  solution  in  the  proportion  of  2£  solution  to  1  of  slime,  by 
weight.  The  solution  contains  0.05%  KCy*.  Agitation  continues 
for  six  hours.  The  vat  is  then  filled  until  there  is  3J  of  solution  to 
1  of  slime;  this  is  well  stirred  and  then  allowed  to  settle.  Settling 
and  decantation  consumes  eight  hours.  This  part  of  the  pro- 
cess is  hastened  by  the  use  of  lime,  which  is  added  to  the  feed  of 
the  tube-mills. 

The  lime  has  two  functions,  one  of  them  chemical,  the  other 
physical.  By  virtue  of  the  first  it  neutralizes  the  sulphuric  acid 
and  decomposes  the  ferric  sulphate  contained  in  the  ore,  and  due 
to  oxidation.  Such  oxidation  may  have  occurred  in  parts  of  the 
lode  before  it  was  mined,  or  it  may  have  been  developed  by  sub- 
sequent contact  with  the  air  in  its  passage  to  the  mill  or  during 
treatment.  The  lime  serves  in  this  way  to  protect  the  cyanide 
of  potassium  or  sodium,  as  the  case  may  be.  In  slaking,  the 
calcium  oxide  (CaO)  takes  up  water  to  form  the  hydroxide 
(Ca(OH)2)  which  dissolves  in  water  to  the  extent  of  one  part  in  800. 
Lime  is  preferable  to  caustic  soda,  for  this  particular  purpose, 
because  the  calcium  carbonate  is  insoluble  in  water,  while  the  sul- 
phate is  but  slightly  soluble,  so  that  they  do  not  accumulate  in  the 
cyanide  solution,  as  is  the  case  with  the  corresponding  sodium 
salts  where  NaOH  is  used  as  the  neutralizing  agent.  Soluble 
carbonates  are  also  precipitated  by  it,  leaving  caustic  alkali  in 
solution,  thus: 

C02  +  Ca(OH)2  =  CaCO3  +  H2O. 
Na2C03  +  Ca(OH)2  =  CaCO3+  2NaOH. 

By  reason  of  its  physical  function  in  the  mill,  lime  coagulates 
slime,  so  as  to  cause  settling  of  the  particles.  The  effect  is  complex. 


*Spdium  cyanide  is  used,  but  all  calculations  are  made  in  terms  of  the  equivalent  potassium 
cyanide.  100  Ib.  NaCy  is  equal  to  128  Ib.  KCy,  therefore  in  practice  eight-tenths  of  NaCy 
does  the  work  of  one  unit  of  KCy.  The  chemical  action  is  the  same,  the  lesser  freight  on  the 
more  concentrated  form  of  the  cyanide  making  the  sodium  preferable  to  the  potassium  salt. 


120  RECENT  CYANIDE  PRACTICE. 

Much  of  the  material  classed  as  slime  is  of  a  colloid  nature — indeed 
slime  has  been  recently  labeled  a  'colloid  hydrate.'  Such  matter  when 
brought  into  contact  with  pure  water  becomes  almost  gelatinous, 
and  therefore  impervious  to  solution.  There  are  several  sub- 
stances, notably  alum,  acids,  soap,  and  lime,  which,  when  added 
to  the  turbid  water,  cause  the  gelatinous  matter  to  coagulate  or 
flocculate,  so  as  to  produce  a  separation  into  distinct  agglomerations. 
Further,  minute  particles  of  ore,  whether  slimy  or  not,  if  suspended 
in  water  and  refusing  to  settle,  develop  a  tendency  to  subside 
when  lime,  alum,  and  other  substances  are  introduced.  Although 
imperfectly  understood,  these  reactions  are  used  largely  both  in 
metallurgy  and  in  agriculture. 

The  slime  settles  rapidly;  within  two  minutes  there  is  an  inch 
of  clear  water.  This  clear  solution  is  decanted  and  passes  to  the 
filter- vat,  the  bottom  of  which  is  provided  with  two  or  three  feet 
of  sand  on  the  top  of  burlap.  This  removes  any  remaining  trace 
of  slime,  cleaning  the  solution  so  that  it  is  fit  to  go  to  the  precipita- 
tion-house. 

Returning  to  the  treatment-vat;  the  slime  remaining  after 
decant ation  undergoes  further  agitation.  The  vat  is  filled  with 
a  0.03%  solution  and  agitation  ensues  for  1J  hours.  Then  follow 
three  more  successive  washes.  The  vat  is  then  filled  for  the  fifth 
time  and  the  mixture  is  thrown  by  a  centrifugal  pump  into  a  deep 
settling-vat.  Five  of  the  treatment  charges  go  to  one  of  these  vats, 
of  which  there  are  six,  each  being  20  ft.  deep  and  34  ft.  diameter, 
with  a  capacity  of  450  tons.  The  successive  charges  from  the 
treatment-vat  are  fed  into  one  settling-vat  until  it  is  full  of  slime, 
for  as  fast  as  the  solution  gathers  on  top  it  is  run  off,  just  sufficient 
time  being  given  for  clarification.  This  clarified  solution  is  so  poor 
in  gold  and  silver  that  precipitation  is  not  attempted,  the  solution 
being  used  as  the  first  of  the  washes  in  the  treatment- vat. 

The  new  mill  contains  three  tube-mills.  All  of  them  were 
made  by  Krupp,  at  Essen.  The  No.  3  mill  is  19  ft.  8  in.  long 
with  3  ft.  11  in.  diam.;  No.  4  is  4  ft.  11  in.  diam.,  and  23  ft. 
9  in.  long,  while  No.  5  is  of  the  same  diameter  as  the  last,  but  26 
ft.  3  in.  long.  The  smallest  of  the  tubes  is  found  to  do  most  work 
per  horsepower  required.  In  Western  Australia  the  tubes  or  grit- 
mills  (as  they  are  often  called)  have  been  cut  down  to  a  length  of 
13  ft.,  but  the  ore  at  Kalgoorlie  is  softer,  so  that  grinding  is  more 
quickly  accomplished  than  at  El  Oro.  The  time  required  is 


CYANIDE  PRACTICE  AT  EL  ORO—I.  121 

determined  directly  by  the  hardness  of  the  rock,  for  the  ore  is  fed  at 
the  upper  end  and  makes  its  exit  at  the  lower,  > through  a  screen. 
Of  the  three  types  of  tube-mills,  the  Abbe  can  be  filled  more  than 
half  full ;  this  cannot  be  done  with  the  Krupp  mill  because  it  both 
fills  and  discharges  at  the  centre.  The  Davidsen  has  central  feed 
but  peripheral  discharge,  while  in  the  Abbe  mill  this  is  reversed, 
the  feed  being  peripheral  and  the  discharge  central.  The  last 
mentioned  is  built  in  sections  and  the  driving  is  done  on  tires 
and  by  gears  which  circle  the  exterior  of  the  shell,  like  a  Bruckner 
furnace.  The  Krupp  tube  is  made  of  wrought-iron  sheets,  welded; 
it  runs  on  trunnions  placed  at  one  end,  so  that  the  shell  does  not 
come  into  play  as  regards  the  driving  of  the  machine. 

The  lining  of  tube-mills  is  an  important  matter.  Chilled  cast- 
iron,  both  that  imported  from  Krupp 's  works  and  that  made  by 
El  Oro  company  itself,  has  been  tried;  the  latter  costing  one-half 
the  former  and  giving  equal  wear  weight-f  or- weight.  Krupp 's 
lining  is  from  f  to  one  inch  thick,  El  Oro  lining  is  1J  in.  thick. 
Nevertheless,  it  is  the  intention  of  the  manager*  to  substitute 
silex,  a  natural  flint  with  characteristic  conchoidal  fracture;  it  is 
whittled  into  shape  in  Germany  before  shipment,  arriving  in  sec- 
tions 2^  in.  thick,  4  in.  wide,  and  6  in.  long.  The  pebbles  that  do 
the  grinding  come  from  the  coast  of  Denmark.  They  vary  in  size 
from  that  of  an  egg  to  that  of  a  fist,  the  average  being  about  three 
inches  in  diameter.  They  wear  well,  6  Ib.  of  pebbles  being  abraded 
during  the  grinding  of  one  ton  of  sand;  the  consumption  of  lining 
being  1.6  Ib.  An  attempt  is  being  made  to  select  some  of  the  flinty 
quartz,  such  as  occurs  in  the  low-grade  ore  of  the  mine,  to  serve 
as  grinding  material.  This  seems  wise;  if  the  hard  portions  of  the 
ore  can  be  used  to  grind  the  soft,  the  economy  is  obvious. 

At  the  time  of  my  visit,  No.  3  tube  was  being  driven  at  the 
rate  of  31  rev.  per  min.,  while  No.  4  and  No.  5  made  29  revolutions. 
The  duty  of  the  individual  tube-mills  cannot  be  stated;  172  tons 
of  the  coarsest  sand  from  the  new  100-stamp  mill  is  re-ground 
from  35  to  150-mesh,  or  finer,  by  the  three  tubes.  In  addition, 
85  tons  per  day  of  the  coarsest  of  the  40-mesh  sand  coming  from 
the  old  100-stamp  mill  is  reduced  to  the  same  condition,  making 
the  total  work  of  the  three  tubes  257  tons. 

The  tube-mills  get  everything  above  150  mesh,  as  separated 
by  cone  classification.  The  aim  is  to  grind  to  150  mesh  and  this 

*Robert  M.  Raymond,  to  whom  I  am  indebted  for  much  valuable  information 


122  RECENT  CYANIDE  PRACTICE. 

is  accomplished  as  nearly  as  the  capacity  of  the  plant  will  permit. 
Any  oversize  is  returned — as  already  described — for  re-grinding. 
The  cyanide  treatment  is  based  on  making  a  product  of  sand  as 
nearly  150-mesh  as  possible,  while  the  200-mesh  and  finer  are 
treated  as  slime.  This  tube-mill  practice  has  steadily  gained  in 
importance,  the  tendency  being  to  treat  a  larger  proportion  of  the 
product  from  the  stamps  and  to  augment  their  crushing  capacity, 
while  enlarging  the  cyanide  annex.  This  is  a  proper  way  of  meeting 
the  necessities  of  a  mine,  the  output  of  which  increases  in  tonnage 
as  the  grade  declines. 


CYANIDE  POISONING 

(September  29,  1906) 

*In  cases  of  poisoning,  everything  depends  on  prompt  action, 
for  the  chance  of  recovery  is  extremely  small  after  the  lapse  of  a 
very  few  minutes  if  a  fatal  dose  has  been  taken.  One  person 
should  be  dispatched  for  the  nearest  medical  assistance  that  is 
available,  but  no  delay  in  treatment  should  be  permitted  to  occur 
on  this  account.  The  first  care  must  be  to  neutralize  the  rapid 
poison  by  the  antidote,  and  then  to  empty  and. wash  out  the 
stomach  as  soon  and  as  completely  as  possible. 

The  antidote  consists  of  two  solutions  sealed  up  in  bottles, 
and  a  sealed  powder.  The  two  solutions  are  to  be  first  mixed 
together  in  the  tin  vessel  in  which  they  are  packed,  by  breaking 
off  the  sealed  ends  of  the  bottles.  The  tube  containing  the  pow- 
der is  also  to  be  broken  and  the  whole  of  the  powder  added  to  the 
mixture,  and  the  dose  is  to  be  administered  as  soon  as  can  poss- 
ibly be  done.  If  the  patient  is  still  conscious,  he  must  drink  the 
antidote  at  once  without  waiting  for  the  insertion  of  the  stomach 
tube,  but  if  not  conscious,  or  not  responsible,  then  a  small  gag  must 
be  firmly  inserted  between  his  teeth,  so  as  to  prevent  the  stomach 
tube  from  being  bitten  off,  and  the  tube  is  then  to  be  passed  down 
his  throat  and  into  his  stomach.  The  antidote  is  to  be  poured 
down  the  tube,  and  is  then  to  be  followed  by  some  water. 

In  any  case,  either  before  or  after  the  antidote  has  been  taken, 
the  stomach  tube  is  to  be  inserted,  and  about  half  a  pint  of  water 
is  to  be  poured  down  it,  the  patient  being  placed  in  a  reclining 
position,  a  little  raised  from  the  ground.  The  insertion  of  the  tube 
may  produce  vomiting;  this,  however,  is  entirely  favorable  to 
the  course  of  the  treatment.  When  the  last  of  the  water  is  placed 
in  the  funnel,  and  before  it  has  all  descended  into  the  tube,  the 
funnel  end  of  the  latter  is  to  be  lowered  so  as  to  cause  the  tube 
to  act  as  a  syphon,  and  the  stomach  emptied  as  much  as  possible 
of  its  contents.  Fresh  water  is  to  be  poured  down  the  tube,  and 
the  stomach  again  emptied,  and  this  is  to  be  repeated  several 
times,  so  as  to  thoroughly  wash  out  the  stomach.  When  this 
has  been  done,  the  tube  can  be  withdrawn. 

If  the  tube  be  not  at  hand,  every  endeavor  must  be  made 


•From  the  Monthly  Journal  of  the  Chamber  of  Mines,  Western  Australia. 


124  RECENT  CYANIDE  PRACTICE. 

to  induce  vomiting  after  the  administration  of  the  antidote,  while 
an  equal  endeavor  must  be  made  to  cause  the  patient  to  swallow 
more  of  the  antidote  between  the  intervals  of  vomiting,  if  the 
administration  be  not  already  and  completely  made. 

Vomiting  may  be  induced  by  an  emetic,  like  mustard,  or 
by  tickling  the  back  of  the  throat  with  a  clean  feather,  or  a  piece 
of  clean  india  rubber  tube,  or  the  finger.  An  ample  quantity 
of  warm  water  should  be  swallowed  and  vomited,  so  as  to  wash 
out  the  stomach  as  in  the  previous  case.  Should  warm  water 
not  be  at  hand,  cold  water  may  be  employed  in  its  place. 

As  soon  as  the  stomach  has  been  satisfactorily  emptied  and 
washed,  and  the  stomach  tube  withdrawn,  steps  should  be  taken 
to  bring  about  artificial  respiration.  Should  the  patient  appear 
to  be  in  a  state  of  collapse,  and  his  breathing  have  ceased  to  be 
noticeable,  the  application  of  smelling  salts  or  of  ammonia  to  his 
nostrils  may  itself  induce  breathing  again;  but  if  this  be  not  im- 
mediately successful,  the  patient  should  be  treated  as  is  done 
in  cases  of  partial  drowning  or  suffocation. 

Medical  assistance  should  by  this  time  have  arrived;  indeed, 
if  the  patient  be  conscious,  there  is  now  great  hope  that  the  worst 
effects  of  the  poison  will  have  passed  off,  particularly  if  the  details 
of  the  treatment  have  been  all  carried  out,  for  cyanide  poisoning 
is  usually  fatal  within  twenty  minutes. 

The  package  for  treatment  should  consist  of  a  tin  vessel 
with  lid,  in  which  are  packed: 

(a)  A   hermetically   sealed   bottle,    containing   7£   grams   of 
ferrous  sulphate  dissolved  in  30  c.c.  water;  and 

(b)  A   hermetically   sealed   bottle,    containing    1^   grams   of 
caustic  soda  dissolved  in  300  c.c.  water;  and 

(c)  A  tube  containing  two  grams  of  magnesia. 

There  should  be  also  a  gag  for  the  purpose  of  opening  the 
clenched  mouth  of  an  unconscious  person,  and  a  stomach  tube, 
that  can  be  passed  through  the  gag  and  down  into  the  oesophagus 
into  the  patient's  stomach.  This  is  very  easy  to  effect,  but  sev- 
eral persons  in  charge  of  the  plant  should  receive  instructions 
from  the  nearest  medical  man  as  to  how  to  insert  a  stomach  tube  so 
that  they  may  know  how  to  use  it  should  occasion  at  any  time  arise. 

The  apparatus  should  never  be  allowed  to  be  removed  from 
its  place,  but  always  kept  complete  and  ready  for  an  emergency. 
It  is  advisable  to  keep  it  in  duplicate,  in  prominently  marked 
positions  in  the  works. 


CYANIDE  PRACTICE  AT  EL  ORO— II 
'BY  T.  A.  RICKARD 

(October  6,  1906) 

A  few  scattered  notes  on  El  Oro  mill  may  be  worth  recording. 
The  bolts  of  the  battery  frames  are  coupled. by  washers;  these  are 
6  to  10  in.  long  and  from  2£  to  3  in.  wide;  they  connect  two  bolts 
and  hold  them  firm.  If  one  gets  loose,  the  other  holds  it  in  grip 
and  prevents  movement. 

The  guides  are  made  at  the  company's  foundry,  of  cast  iron; 
instead  of  being  sectional  with  bolts,  they  are  one  solid  piece. 
Each  stamp  has  its  own  guide  and  a  right-angle  plate,  to  keep  it 
in  proper  place  and  line.  The  wear  is  slight  and  therefore  the 
stamp  works  smoothly;  there  is  less  heating  than  with  wooden 
guides. 

The  mortar  is  a  development  of  the  anvil-block.  This  is  an 
excellent  mode  of  construction,  if  properly  done.  I  know  of 
one  case  — not  in  Mexico — where  trouble  was  caused  by  the  anvil- 
block  being  constructed  so  that  it  did  not  rest  perfectly  true  on 
the  cement  foundation ;  to  remedy  this  it  was  the  custom  to  shim 
the  concrete  block  with  a  little  cement;  when  this  last  broke  and 
crumbled,  there  was  a  movement  of  the  mortar  itself.  At  El  Oro, 
the  mortar-block  is  made  extra  heavy,  combining  to  some  extent 
the  anvil  in  itself,  with  a  base  three  feet  wide  and  a  bottom  13  in. 
thick;  this  is  placed  upon  a  concrete  foundation,  with  a  piece  of 
quarter-inch  rubber  belt  between. 

At  El  Oro,  cones  are  superior  to  spitzkasten;  the  sizing  tests 
have  proved  this  abundantly,  the  separation  by  the  cones  being 
much  sharper.  The  circulation  and  agitation  of  slime  are  aided 
by  six  pumps  which  are  the  Butters  modification  of  the  Gwynne 
pump,  such  as  is  used  in  the  London  dock-yards.  They  are  of  the 
centrifugal  type ;  compressed  air  is  introduced  to  effect  aeration 
of  the  solution.  The  chief  advantage  of  the  Butters  modification 
is  that  all  wearing  parts  are  readily  removable.  Each  pump 
makes  1,300  rev.  per  min.  and  in  that  period  handles  4£  tons 
(3i  tons  being  solution)  of  slime. 

The  vats  are  all  made  of  steel  plates,  3/16  in.  thick  on  sides, 
with  J-in.  bottoms.  Redwood  laid  down  at  El  Oro  comes  to  the 


126  RECENT  CYANIDE  PRACTICE. 

same  cost,  but  the  steel  is  more  durable  and  makes  a  tighter  vat 
in  the  climate  of  central  Mexico.  The  vat  does  not  dry  if  empty, 
there  are  no  staves  to  check,  and  no  absorption  of  solution. 

In  the  precipitation  house,  there  is  used  a  device  introduced 
independently  by  W.  K.  Betty  in  South  Africa  and  by  Alfred 
F.  Main  at  El  Oro;  I  refer  to  a  drop-drip  of  KCy  (2J%  solution) 
over  the  head  compartment  of  each  zinc-box  that  is  precipitating 
from  the  weakest  solution  namely,  that  coming  from  the  treatment 
of  slime.  This  drip  makes  the  zinc  more  active,  so  that  a  pre- 
cipitation of  precious  metal  is  obtained  in  a  manner  usually  un- 
attainable from  so  weak  a  solution,  that  is,  one  containing 
only  0.02%  KCy.  Still  weaker  solutions  are  success- 
fully precipitated  in  which  the  quantity  of  KCy  is  so  small  as  not 
to  be  detected  by  the  ordinary  silver  nitrate  test. 

The  method  of  dipping  the  zinc  shaving  in  lead  acetate  (to 
aid  precipitation)  is  not  employed  at  El  Oro  because  lead  acetate 
is  used  at  another  stage  of  the  process,  as  already  explained. 
Zinc  fume  was  tried,  but  it  was  ineffective  with  such  weak  solutions. 
Great  care  is  taken  with  the  zinc  shaving,  to  cut  it  in  thin  but 
tough  filaments,  not  so  crinkly  as  to  break  easily  in  handling. 
The  shaving  is  laid  in  the  boxes  most  carefully,  so  as  to 
avoid  any  tendency  to  channeling.  The  El  Oro  plant 
is  the  only  one  of  its  size  where  acid  treatment  is  not 
used.  From  the  boxes  the  zinc  is  sent  through  launders, 
to  be  carefully  screened,  while  it  is  also  being  washed  with  fresh 
water.  Then  it  is  pumped  into  two  filter-presses  until  they  are 
full,  the  charge  being  equivalent  to  19,000  oz.  of  bullion.  The 
effluent  solution  is  returned  to  the  sump,  the  cakes  in  the  press 
are  washed  and  then  dried  by  steam,  the  steam  heating  the  iron, 
of  the  frame  sufficiently  to  dry  the  cake  inside.  The  cakes  are 
dried  to  such  a  consistence  as  will  facilitate  fluxing  before  bri- 
quetting;  they  fall  into  a  car  and  are  then  mixed  with  the  fluxes 
needed  for  melting;  the  mixture  is  fed  into  a  briquetting  machine, 
making  round  bricks  3J  in.  thick  with  3  in.  diam.  These  are 
dried  before  being  thrown  into  the  melting  pot,  from  which  bars 
of  1,000  oz.  are  cast.  The  Mexican  workmen  are  compelled  to 
remove  their  clothes  after  work,  before  passing  to  the  outer  room. 
The  precipitation  room  has  a  cement  floor  and  the  furnace  has  a 
dust-chamber. 


CYANIDE  PRACTICE  AT  EL  ORO—IL  127 

The  development  of  milling  at  El  Oro  emphasizes  the  rela- 
tive, importance  of  the  cyanide  annex  in  the  modern  wet  treatment 
of  precious-metal  ore;  the  annex  to  the  new  mill  required  an  ex- 
penditure a  little  over  twice  the  cost  of  the  new  100-stamp  mill 
itself.  The  tendency  is  to  increase  the  percentage  that  is  re- 
ground,  the  perfection  of  the  extraction  being  closely  determined 
by  the  fineness  of  comminution.  At  the  time  of  my  visit  the 
aim  was  to  make  two  products;  sand,  as  near  150-mesh  as  possible 
(and  a  decreasing  percentage  even  of  that)  and  slime,  that  is, 
all  below  200-mesh.  Of  course,  the  sand,  even  when  re-ground, 
is  different  from  the  clay  despite  equality  in  size  of  particles; 
the  grains  of  'sand'  are  sharp  as  against  those  of  a  mud  (slime) 
rendered  impalpable  by  absence  of  sharp  edges.  'Sand'  how- 
ever fine,  filters  well,  while  'slime'  will  not  filter  at  all;  it  packs  like' 
glue.  On  the  other  hand,  by  reason  of  the  relatively  larger  surface 
presented  by  minute  particles,  chemical  action  on  the  precious 
metals  is  almost  instantaneous.  How  necessary  re-grinding  is, 
was  shown  by  a  simple  experiment  made  by  Mr.  S.  H.  Pearce. 
Sand,  after  ordinary  cyanide  treatment  at  the  old  mill,  where 
there  is  no  re-grinding,  was  dissolved  in  aqua  regia,  but  the  'purple 
of  Cassius'  test,  with  stannous  chloride,  gave  no  precipitate  what- 
ever, the  gold  being  effectively  locked  within  the  grains  of  sand. 
The  assay  of  the  sand  gave  $4.50  per  ton.  Hence  the  need  for 
re -grinding. 

The  accompanying  record  of  tests  will  prove  interesting  to 
those  engaged  in  cyanide  work.  Looking  at  Fig.  11,  it  will  be 
noted  that  the  legend  explains'  the  graphic  representation  of 
two  sizing  tests.  At  the  time  of  these  tests,  a  2J-in.  chuck-block 
was  used,  but  it  was  too  low  to  have  much  effect  on  the  degree 
of  fineness  of  the  product ;  during  the  test  the  stamp -discharge 
was  as  through  28  mesh.  Under  these  conditions  the  load  on 
the  tube -mills  and  on  the  plant  became  too  heavy,  so  that  finer 
screens  were  substituted  shortly  afterward.  In  the  diagram  (taken 
from  the  paper  by  Caetani  and  Burt,  already  mentioned)  the 
ordinates  represent  the  size  of  the  screen  and  the  abscissae  the 
percentage  retained  on  each  of  the  screens.  In  the  legend  "Thro' 
250  mesh"  should  read  "through  200  mesh." 

The  use  of  the  term  sand-index,  to  be  seen  in  the  note  appear- 
ing on  the  diagram,  requires  explanation.  Caetani  and  Burt 
employ  it,  and  it  represents  one  of  the  most  valuable  features 


S    a".t  § 


CYANIDE  PRACTICE  AT  EL  ORO—II. 


129 


of   their    paper.     The    problem    was    the    following.     Given    two 
sands  of  the  following  analysis: 


Mesh 

1st  sand  . . 
2nd  sand. . 


On  20       On  40          On  100         On  200 


10 
5 


30 
15 


25 
45 


15 


Through  200 
or  slime 

30 
•   20 


Which  of  these  two  sands  is  the  finest?  Caetani  answers 
the  question  from  the  economic  point  of  view,  thus:  It  is  desired 
to  know  the  fineness  of  a  sand  for  the  reason  that  the  finer  the  sand, 
the  better  the  extraction  obtained.  Therefore  the  maximum 
possible  extraction  on  a  sand  of  given  composition  is  a  number 
proportional  to  its  fineness,  considered  from  an  economic  standpoint. 
As  at  El  Oro  one  can  a  priori  calculate  exactly  the  extraction 
from  a  sand  when  a  sizing  test  has  been  made,  therefore  one  can 
calculate  the  index  and  represent  thereby  with  one  number  what 
would  otherwise  have  to  be  indicated  by  a  tabulation  consisting 
of  14  numbers.  In  the  examples  quoted  at  the  beginning  of  the 
paragraph,  the  second  sand  is  finer  than  the  first,  although  it 
contains  less  slime. 

REPORT  OF  CYANIDE  DEPARTMENT,  SEPTEMBER,  1905. 

MILL  NO.    1. 


vjn 

Assay 

Indi- 

Assav 

Indi- 

value 

cated 

value 

cated 

Classification'  — 

Tons 

per 

extrac- 

per 

extrac- 

treated. 

ton. 

tion. 

ton. 

.      tion. 

°/i 

•)• 

$ 

% 

$ 

% 

Coarse  Sand   .  .  . 

,    29 

.23 

2,552 

9.46 

54.33 

1.73 

27.17 

Fine  Sand  

,    25 

.57 

2,233 

7.86 

72.14 

1.57 

45.86 

Slime  

.    45 

.20 

3,947 

9.04 

93.58 

2.03 

82.26 

Total 100  8,732          8.86  76.50  1.83  58.99 

REMARKS. — Old  mill  built  before  re-grinding  was  adopted.  Fine  sand 
poorer  than  coarse  because  it  contains  less  gold  open  to  attack.  Slime 
richer  in  silver  by  presence  of  sulphide. 


Sand 24.12 

Slime  .  .75.88 


2,527 
7.949 


MILL  NO.   2. 

8.28 

7.68 


83.94 
92.45 


90.28 


1.59 
1.64 

1.63 


65.41 
78.05 


75.08 


Total 100  10,476 

REMARKS. — New    mill    includes    systematic    scheme    of    re-grinding,    as 
hown  by  increased  proportion  of  slime.     Better  extraction  on  slime  raises 
general  result  to  a  satisfactory  figure. 


130  RECENT  CYANIDE  PRACTICE. 

The  Esperanza  mill  had  120  stamps  when  the  present  com- 
pany took  it  over,  in  1904.  It  was  deemed  advisable  to  increase 
the  capacity  at  the  least  possible  cost,  so  15  Huntington  mills 
(each  of  5-ft.  diam.),  were  added,  with  the  idea  of  re-grinding  be- 
fore cyanidation.  This  was  tried,  but  it  was  found  necessary  to 
place  the  Huntingtons  above  the  stamp-batteries,  which  necessi- 
tated elevating  the  pulp.  It  being  therefore  difficult  to  distribute 
the  pulp  to  the  Huntington  mills,  it  was  finally  decided  to  use  the 
latter  machines  for  first  grinding,  in  association  with,  instead  of 
in  succession  to,  the  stamps. 

The  crude  ore  passes  over  a  IJ-in.  grizzly  before  it  reaches 
the  rock-breakers;  after  being  crushed  by, them,  the  ore  goes  over 
a  f-in.  grizzly,  the  undersize  being  allotted  to  the  Huntingtons 
and  the  oversize  to  the  stamps.  The  batteries  are  provided  with 
60-mesh  screens;  while  the  pulp  issuing  from  the  Huntington 
mills  goes  through  an  angle-slot  screen  equivalent  to  60-mesh, 
but  65%  of  the  product  will  pass  200  mesh. 

Of  the  15  Huntingtons,  six  are  now  used  as  first  grinders 
on  lowr-grade  sulphide  ore,  the  product  being  sized  and  distributed 
to  six  Wilfley  tables,  the  tailing  from  which,  after  classification, 
passes  down  blanket  sluices  before  finally  reaching  the  cyanide 
vats.  The  concentrate  from  the  Wilfleys  and  that  washed  from 
the  blankets,  goes  to  the  smelter  at  Aguascalientes. 

The  other  nine  Huntingtons  treat  oxidized  ore,  which,  after 
being  ground,  goes  to  the  cyanide  annex.  The  cost  of  steel  and 
repairs  to  wearing  parts  amount  to  34  centavos  per  ton;  labor 
averages  15  to  20  cv.  per  ton.  The  muller  shells  and  die- 
ring  are  made  of  roll  steel  manufactured  by  the  Midvale  Steel 
Co.,  of  Philadelphia.'  This  is  a  soft  metal  and  is  susceptible  of 
being  kept  to  shape;  it  can  be  used  until  worn  out,  and  is,  there- 
fore, economical.  Each  Huntington  mill  has  its  own  motor; 
it  has  proved  itself  to  be  the  best  machine  for  reducing  the  ore 
to  a  certain  point — say,  60  mesh — beyond  which,  for  finer  grind- 
ing, it  is  not  economical. 

The  sand  undergoes  treatment  for  100  hr;  for  it  is  found 
that  extraction  ceases  then.  Aeration  is  effected  by  a  perforated 
pipe  discharging  over  the  return-solution  vat;  yet  there  is  no 
such  loss  of  KCy  as  might  have  been  expected.  The  former  col- 
lecting vats  are  now  used  for  treatment;  there  is  less  aeration 
and  less  mixing,  but  there  is  a  great  gain  in  the  capacity  of  the 


CYANIDE  PRACTICE  AT  EL  ORO—II.  131 

plant  without  interference  with  effective  percolation.  A  vacuum- 
pump,  for  withdrawing  the  enriched  solution,  is  used  only  at  the 
close  of  the  operation.  Sodium  cyanide,  NaKCy,  is  the  chemical 
employed;  it  is  guaranteed  equal  to  125%  active  KCy,  ranging 
from  124  to  128%.  The  enriched  solution,  before  precipitation 
in  zinc-boxes,  is  rarely  higher  than  $2.20  in  gold.  Fresh  cyanide, 
in  crystals,  is  added  to  the  head  of  the  zinc-boxes,  sometimes  in 
quantities  sufficient  to  keep  the  solution  up  to  standard  strength. 

There  are  no  amalgamating  plates,  and  no  mercury  is  used 
in  the  Esperanza  plant.  This  is  an  interesting  divergence  from 
El  Oro  practice. 

During  September,  1905,  the  output  of  the  mine  consisted 
of  5,280  tons  of  shipping  ore  and  12,000  tons  of  milling  ore,  hav- 
ing together  a  value  of  $780,385  U.  S.  currency.  The  extraction 
in  the  mill  was  91.64%  of  the  gold  and  52.92%  of  the  silver  in  the 
crude  ore. 


COPPER  IN  CYANIDE  SOLUTIONS 

(October  6,  1906) 

The   Editor: 

Sir — As  to  copper  in  cyanide  solutions,  finding  facts  here 
at  variance  with  those  published  in  your  issue  of  September  1, 
I  thought  an  account  of  our  practice  here  would  be  of  interest 
as  well  as  our  manner  of  making  pure  bullion  from  a  zinc-box 
product  high  in  copper. 

The  gold-bearing  ore  consists  of  hematite  and  clay  in  about 
equal  proportions  and  0.75-lb.  copper.  On  account  of  the  clay, 
roasting  is  required  to  effect  dehydration.  Without  such  dehydra- 
tion the  treatment  of  slime, which  amounts  to  over  50%,  would  be 
impossible,  either  by  filter-pressing  or  decantation.  The  latter 
is  the  method  we  employ,  using  shallow  vats  19  in.  high,  which 
settle  completely  in  four  hours,  including  the  decantation  of  the 
clear  solution.  The  loss  in  cyanide  is  about  four  pounds  per  ton, 
with  a  solution  containing  1J  Ib.  cyanide. 

The  zinc-boxes,  of  eight  compartments  each,  show  pure 
copper  in  the  last  two  compartments,  and  gradually  turn  black  to- 
ward the  head.  The  copper  is  not  loose  and  spongy,  but  adheres 
firmly,  and  to  all  appearances  looks  like  pure  copper  shaving. 
I  am  inclined  to  believe  that,  in  this  instance  at  least,  copper 
helps  in  the  precipitation  of  gold  and  silver  because  a  copper 
hue  on  the  zinc  has  always  been  a  proof  that  the  sump  assays 
only  a  trace  in  gold.  These  coppered  shavings  when  treated 
with  sulphuric  acid,  and  then  cupelled,  yield  gold  1,000  fine; 
so  that  the  sump  must  be  free  from  silver. 

We  have  found  it  necessary  on  but  two  occasions  during  the 
past  two  years  to  dress  the  zinc  in  the  boxes  and  then  the  last 
compartments  were  not  coated  with  appreciable  amounts  of 
copper.  We  simply  clean  up  the  first  and  part  of  the  second 
compartments  every  month,  unless  previously  gold  slime  has  so 
accumulated  that  it  retards  the  proper  flow  of  solution. 

The  short  zinc  is  not  removed.  We  find  in  this  fact  a  con- 
tradiction to  many  authors  who  claim  short  zinc  to  be  inert. 
The  fact  that  we  can  return  short  zinc  with  no  accumulation  of 
such  product,  is  a  proof  of  its  precipitating  qualities.  Only  what 
can  be  washed  through  a  20-mesh  screen  is  treated  with  acid  and— 


COPPER  IN  CYANIDE  SOLUTIONS.  133 

this  before  acid  treatment — is  separated  by  stirring  in  water 
and  decanting  the  suspended  slime"  until  only  a  coarse  granular 
mass  is  left.  The  latter  is  treated  with  sulphuric  and  the  former 
with  hydrochloric  acid.  The  slime  contains  a  large  percentage 
of  calcium  carbonate,  which  forbids  the  use  of  sulphuric  acid 
on  account  of  the  regulus  that  would  be  formed  in  melting  and 
on  account  of  adulteration  of  precipitate  with  sulphate  of  lime. 

Ten  parts  of  the  coarse  or  12  parts  of  the  slime  after  acid 
treatment  are  melted  in  a  graphite  crucible  with  about  eight  parts 
of  a  mixture  of  26  litharge,  20  borax  glass,  and  one  nitre.  The 
melting  must  be  quickly  performed  to  prevent  formation  of  too 
much  lead  from  the  action  of  the  graphite  in  the  crucible,  and 
unless  considerable  experience  is  obtained  as  to  the  proper  time 
and  heat,  a  flux  consisting  of  equal  parts  of  bicarbonate  of  soda 
and  borax  glass  would  be  safer.  The  use  of  litharge,  on  account 
of  its  rapid  shrinking  before  complete  melting,  allows  -of  several 
fillings  before  fusion.  The  flux  and  charge  are  mixed  after  wetting 
sufficient  to  prevent  dusting. 

The  smaller  bars  resulting  from  different  melts  are  now  ready 
for  refining  as  follows:  Place  inside  of  No.  35  graphite,  crucible 
a  Battersea  P  crucible  so  that  the  bottoms  of  each  touch.  To 
accomplish  this,  the  graphite  crucible  must  be  slightly  clipped 
inside  for  about  an  inch  from  the  top.  Melt  the  bars  in  the  clay 
crucible  and  then  add,  from  time  to  time,  a  little  nitre  until  the 
metal  is  covered  with  slag,  which  should  then  be  skimmed  by 
means  of  a  small  crucible  (10  grams)  held  with  tongs.  Repeat 
the  adding  of  nitre  and  skimming  until  the  skimmings  show 
but  little  lead  and  the  bullion  looks  bright.  On  an  average, 
the  bars  which  before  refining  are  700  to  800  fine,  yield  by  above 
treatment  bars  of  over  900-  fine. 

In  case  the  soda  flux  is  used,  about  five  per  cent  metallic 
lead  should  be  melted  with  the  bar,  as  without  lead  the  copper 
is  difficult  to  remove.  The  refining  takes  about  an  hour  after 
melting.  If  all  the  melts  are  made,  using  a  clay  crucible  direct, 
bullion  of  985  fine  can  be  produced  in  the  original  melt,  using 
either  litharge  or  soda  flux.  However,  as  I  was  not  able  to  obtain 
larger  clay  crucibles  than  the  Battersea  P  size  and  as  the  heat 
must  travel  through  two  crucibles,  clay  breaking  in  direct  contact 
with  coke,  I  found  it  preferable  to  refine  in  one  melt. 

C.  A.  ARENTS. 

Copperopolis,  Cal.,  Sept.  17. 


ZINC-DUST  PRECIPITATION 

(October  6,  1906) 

The  Editor: 

Sir — After  reading  your  remarks  concerning  zinc-dust  precipi- 
tation I  have  been  inquiring  among  my  professional  friends  and 
from  one  of  them  I  have  secured  information  which  I  feel  sure  will 
interest  others,  as  much  as  it  did  me.  This  engineer  was  super- 
intendent of  a  100-ton  sand  and  slime-plant.  Slime  was  treated 
by  decantation  and  sand  by  percolation,  the  ore  containing  both 
silver  and  gold,  with  over  50%  of  the  value  in  gold. 

The  precipitation  plant  consisted  of  three  15-ton  flat -bottomed 
wooden  tanks,  a  six-inch  self-acting  compressor,  a  four-inch 
triplex-driven  plunger-pump,  and  two  2.5-ton  filter-presses.  One 
of  the  latter  was  a  Johnston  press  with  six-inch  frames.  The  leach 
from  sand  and  slime  ran  to  a  sump  whence  it  was  pumped  to  one  of 
the  three  agitation  vats.  This  pregnant  solution  was  worth  about 
$2  per  ton.  The  compressor  was  started  and  air  pumped  through 
a  j-in.  line  to  a  grating  of  half -inch  pipes  in  the  bottom  of  the  vat. 
These  branch  pipes  were  perforated.  Two  to  four  pounds  of  zinc 
dust  were  added  (an  average  of  3.5  lb.).  and  the  agitation  with  air 
continued  about  twenty  minutes.  The  charge  was  then  pumped 
by  means  of  the  triplex  plunger  through  the  press.  One  press 
held  about  one  month's  product.  In  order  that  the  press  should 
fill  completely,  it  was  the  custom  to  close  the  discharge-cocks 
of  the  frames  in  the  half  nearest  the  inlet,  gradually  opening  them 
as  the  farther  frames  became  filled.  The  plant  treating  the  ore 
produced  a  product  worth  $20  per  lb.,  while  the  plant  treating  old 
tailing  from  a  former  pan-amalgamation  mill  made  a  precipitate 
worth  $8  per  pound. 

This  precipitate  was  treated  with  sulphuric  acid,  roasted 
in  an  iron  muffle  and  melted  in  pots.  The  zinc  dust  costs  5.5 
to  6c.  per  pound  at  the  works.  No  attempt  was  made  to  remove 
the  zinc  oxide  with  ammonia.  The  quantity  of  zinc  used  was 
governed  by  the  value  of  the  barren  solution.  Sometimes  an  in- 
crease of  zinc  made  a  better  precipitation  and  at  other  times  .an 
increase  in  the  strength  of  solution  used  on  the  ores  attained  the 
same  result.  A  twenty-cent  tail-solution  was  considered  very  high. 


ZINC-DUST  PRECIPITATION,  135 

The  precipitation  vats  were  flat-bottomed,  and  this  necessitated 
an  occasional  clean-up,  which  consisted  of  hard  labor  with  hammer 
and  chisel.  This  difficulty  could  be  avoided  by  having  conical- 
bottomed  vats.  About  225  tons  were  precipitated  in  24  hours. 

The  presses  would  stand  a  pressure  of  40  lb.,  although  it  was 
the  custom  to  fill  the  presses  with  as  low  a  pressure  as  possible, 
pumping  the  solution  at  a  rate  barely  sufficient  to  keep  up  with  the 
plant. 

No  naked  flame  should  be  allowed  around  the  press  while 
opening,  and  the  cigarette  smokers  must  be  kept  at  a  distance. 
A  flame  applied  to  the  charge  when  the  press  is  first  opened  will 
explode  the  hydrogen  mixture,  separating  the  frames  and  scatter- 
ing mud. 

Some  years  ago  I  was  shown  the  plant  at  Mercur  and  no  secret 
was  made  of  the  method  of  precipitation,  and  the  same  statement 
applies  to  the  attitude  of  those  in  charge  at  Lead,  South  Dakota. 

MARK  R.  LAMB. 

Goldfield,  Nevada,  September  4. 


ORE  TREATMENT  AT  THE  COMBINATION  MINE, 
GOLDFIELD,  NEVADA 

BY  FRANCIS  L.  BOSQUI 

(October  6  and  13,  1906) 
I.     METALLURGY 

The  Combination  mine,  situated  about  one-half  mile  north- 
east of  the  town  of  Goldfield,  consists  of  ten  full  claims  and  three 
fractions,  aggregating  200  acres.  The  original  discovery  on  Com- 
bination ground  was  the  first  of  any  importance  made  in  the  now 
famous  camp.  The  property  was  acquired  from  prospectors  in 
1903  by  the  representatives  of  two  Eastern  exploration  com- 
panies, who,  after  a  visit  to  one  of  the  outlying  districts,  happened 
to  be  passing  through  the  present  site  of  Goldfield  on  the  way  to 
Tonopah;  and  thus,  at  the  very  outset  of  its  career  as  a  gold  pro- 
ducer, the  Combination  was  blessed  by  the  happiest  accident 
that  can  befall  a  mine — it  passed  into  good  hands.  The  property 
has  since  occupied  a  unique  place  among  the  mines  of  southern 
Nevada.  It  has  been  well  administered;  it  has  had  the  benefit 
of  the  most  approved  and  practical  methods  in  mining  and  met- 
allurgy; and  its  development  has  not  been  hampered  by  stock 
manipulations.  Consequently,  though  the  most -interesting  prop- 
erty in  the  district,  whether  we  consider  its  varied  metallurgical 
problems,  or  its  ratio  of  output  to  small  mill-capacity  and  small 
development,  it  is  the  least  advertised  and  the  least  discussed. 

The  first  shipments  from  the  Combination  were  made  in 
December,  1903.  The  gross  output  of  the  mine  from  the  com- 
mencement of  operations  to  April  1,  1906,  is  as  follows: 

Value  •     Total   Value 

Shipping  ore  (tons) 1,773        $438.24  $776,992.84 

Stamp  bullion  (oz.) 13,584             19.48  264,506.30 

Concentrate  (tons) 230          352.05  80,972.07 

Cyanide  precipitate  (Ib.) 734             45.77  33, 594. 18 

Cyanide  bullion  (oz.) 4,401             16.44  72,346.51 

$1,228,411.90 

The  property  was  a  shipper  from  the  grass-roots.  Almost 
any  grade  of  ore  could  be  segregated  by  rough  screening  and 


ORE  TREATMENT  AT  THE  COMBINATION  MINE.  137 

sorting,  the  practice  being  to  reserve  the  milling  ore  ($25  to  $100) 
in  graded  dumps  until  the  completion  of  a  mill.  In  shipping  it 
was  at  first  necessary  to  haul  the  ore  to  the  railroad,  a  distance  of 
60  miles.  The  costs  of  transportation  and  smelter  treatment 
were  so  high  as  to  emphasize  the  importance  of  treatment  on  the 
ground,  and  an  investigation  was  at  once  commenced  with  a  view 
to  installing  a  reduction  plant 

The  ore  has  been  described  as  a  highly  silicified  dacite  occur- 
ring in  zones  of  fissuring  in  the  decomposed  dacite  constituting 
the  country  rock.  In  the  more  shattered  portions  of  the  ore- 
body  the  dacite  is  almost  entirely  altered  into  quartz,  with  string- 
ers and  patches  of  kaolinized  material.  During  the  progress  of 
the  preliminary  tests,  the  ore  showed  certain  freakish  variations 
which  made  it  difficult  to  decide  upon  a  method  of  treatment. 
The  fineness  of  the  gold,  and  the  almost  entire  absence  of  con- 
centratable  material  in  the  upper  levels  indicated  dry-crushing, 
and  a  testing  plant  for  dry-crushing  was  installed.  But  even 
after  a  long  leaching  with  cyanide  solution,  it  was  still  found 
possible  to  pan  an  appreciable  quantity  of  gold  from  the  residue. 
These  tests  had  scarcely  begun  before  the  gold  in  the  mine  became 
coarser,  and  the  proportion  of  sulphides  increased.  A  series 
of  tests  by  amalgamation,  concentration,  and  cyanidation,  gave 
decidedly  promising  results,  showing  an  average  saving  of  45% 
by  the  first,  5%  by  the  second,  and  about  40%  by  cyaniding  the 
residual  sand  and  slime — a  total  of  about  90%.  Later,  it  devel- 
oped that  certain  portions  of  the  oxidized  ore  carried  a  disquiet- 
ing amount  of  acid — free  sulphuric  and  ferrous  sulphate,  with  here 
and  there  enough  alum  to  make  the  rock  astringent  to  the  taste. 
In  some  of  the  tests  the  ore  was  so  acid  as  to  require  50  Ib.  of  lime 
per  ton  as  a  neutralizer.  But  this  very  acid  ore  was  not  found 
to  be  in  sufficient  quantity  to  affect  the  general  treatment  ser- 
iously; and  in  subsequent  milling  tests  an  average  sample  of  all 
the  accessible  oxidized  ore  was  taken,  and  the  acid  condition 
met  by  using  from  10  to  12  Ib.  lime  per  ton. 

The  results  obtained  in  ore  tests  made  at  Goldfield  in  the 
early  months  of  1904  were  confirmed  during  the  summer  by  mill- 
runs  made  at  an  ore-testing  plant  in  San  Francisco.  The  represen- 
tative test,  which  gave  the  best  results,  was  made  as  follows: 

1.  Crushing  through  40-mesh  wire  screen. 

2.  Plate  amalgamation. 


138 


RECENT  CYANIDE  PRACTICE. 


3.  Concentration  on  a  Frue  vanner. 

4.  Hydraulic   separation   of  slime  in   cone-classifiers. 

5.  Leaching  sand   with   cyanide   solution. 

6.  Agitating  slime  with  cyanide  solution. 

The  best  conditions  for  the  sand  were  found  to  be  eight  days' 
leaching  with  a  0.2%  solution;  while  the  slime  required  four  hours 
with  a  0.15%  solution.  The  following  is  a  record  of  extraction 
from  slime: 

Gold, 
oz. 

Assay  heads " .  .  .' 1 . 20 

Assay  after  1  hr.  agitation 0 . 46 


0.20 
0.14 
0.12 
0.12 
0.13 
0.12 
0.12 


The  amalgamation  plate  and  zinc-box  were  cleaned  up  and 
the  following  results  obtained  from  the  whole  test: 

Indicated  extraction  by  cyanide,  83.4%. 

Actual  extraction  by  cyanide,  77.9%. 

Indicated  total  extraction  by  all  processes,  93%. 

Actual  total  extraction  by  all  processes,  91%. 

On  a  small  scale,  better  results  were  obtained  by  crushing 
to  50-mesh,  and  it  was  found  that  by  sliming  the  whole  product, 
a  still  higher  recovery  might  be  made.  But  the  unproved  effi- 
ciency of  American  tube-mills  at  the  time  the  tests  were  made 
and  the  high  cost  of  power  and  labor  at  Goldfield,  left  the  advan- 
tage in  favor  of  sliming  too  small  to  justify  the  experiment. 

The  mill  was  originally  designed  to  treat  oxidized  ore  only, 
although  in  places  in  the  oxidized  zone  there  were  found  small 
quantities  of  sulphide  ore  which  resisted  mill  treatment  by  ordi- 
nary methods.  But  as  there  was  no  indication  of  the  develop- 
ment of  a  large  amount  of  sulphide  ore  at  the  time  construction 
commenced  on  the  mill,  the  installation  was  allowed  to  proceed. 
It  was  while  the  mill  was  being  built  that  large  shoots  of  sulphide 
ore  were  opened  up  as  the  limit  of  the  oxidized  zone  was  reached, 
and  before  the  end  of  the  year  an  extensive  dump  had  accumulated 
with  an  average  content  of  about  3  oz.  gold.  This  was  reserved 
for  special  treatment,  and  samples  taken  for  investigation. 


ORE  TREATMENT  AT  THE  COMBINATION. MINE.   139 

The  sulphide  in  the  'sulphide  ore'  of  the  lower  levels 
simple  iron  pyrite,  for  the  most  part  finely  disseminated 
following  is  an  analysis  of  the  ore : 

Silica,  70.4%;  alumina,  17.0%;  sulphur,  4.2%;  iron,  8.5%, 
and  copper,  trace. 

Direct  cyanide  treatment  was  tried  in  all  practicable  variations, 
but  without  good  results. 

After  grinding  through  200  mesh  and  agitating  15  hr.  in  a 
0.25%  cyanide  solution,  the  recovery  was  only  60%,  with  a  4-lb. 
cyanide  consumption. 

Roasting  and  leaching  a  20-mesh  product  gave  an  extraction 
of  91%,  with  a  7.2-lb.  cyanide  consumption. 

Roasting  a  20-mesh  product,  re-grinding  to  200-mesh,  and  cya- 
niding  by  agitation  in  a  0.25%  solution  gave  93%  extraction. 

Pan  amalgamation  of  the  roasted  ore  gave  an  extraction  of 
54  per  cent. 

Oil  concentration  (Elmore  process)  of  raw  ore,  with  agitation 
of  tailing  in  cyanide  solution,  gave  90%  extraction  with  a  consump- 
tion of  1\  Ib.  cyanide  per  ton. 

Oil  concentration  followed  by  cyanogen  bromide  treatment 
of  the  tailing  gave  an  extraction  of  96%  from  heads  assaying 
3.48  oz.  gold. 

Chlorination  by  leaching,  using  an  aqueous  solution  of  chlorine 
produced  by  bringing  together  an  0.8%  sulphuric  acid  solution, 
and  a  0.7%  chloride  of  lime  solution,  and  leaching  36  hr.,  gave  a 
recovery  of  40  per  cent. 

Chlorination  by  the  barrel  process,  after  four  hours'  treatment, 
yielded  78  per  cent. 

These  various  methods  were  tried  before  wet  concentration 
because  the  aim  was  to  treat  all  products  on  the  ground  and  avoid 
shipping.  A  combination  of  concentrating  and  cyaniding,  however, 
was  ultimately  considered  the  most  suitable  to  Goldfield  condi- 
tions, and  was  adopted. 

The  ordinary  concentration  of  30  or  40-mesh  product  was  found 
ineffective.  It  did  not  make  a  close  saving  of  the  fine  sulphide, 
which  had  to  be  removed  on  account  of  the  poor  cyanide  recovery 
from  the  raw  sulphide.  It  was  necessary  to  evolve  some  closer 
method  of  recovery  which  would  leave  nothing  for  cyanide  treat- 
ment except  the  finest  particles  that  might  elude  the  most  efficient 
.concentrating  machinery.  The  only  way  to  accomplish  this  was 


140  RECENT  CYANIDE  PRACTICE. 

by  a  series  of  reductions,  and  by  following  each  stage  by  appro- 
priate concentration.  The  sulphide  freed  at  each  stage  of  grinding 
was  at  once  removed  before  the  ore  passed  to  the  next  and 
finer  stage  of  grinding,  and  thus  an  unnecessary  comminution 
was  avoided. 

The  following  mill  test  forms  the  basis  of  the  method  adopted 
in  practice.  The  ore,  assaying  3.01  oz.  gold,  was  crushed  in  stamps 
to  30  mesh  and  passed  over  a  small  Wilfley  concentrator.  This 
yielded  6%  (by  weight)  of  concentrate,  assaying  27.4  oz.  gold. 
The  tailing  was  re-ground  through  60  mesh,  and  re -concentrated, 
yielding  2.11%  concentrate,  assaying  19.8  oz.  gold.  The  60-mesh 
tailing  was  re -ground  through  100  mesh  and  concentrated,  yield- 
ing 0.4%  concentrate,  assaying  20.4  oz.  gold.  The  residue  was 
then  ground  to  200  mesh,  and  passed  over  a  canvas  table,  yielding 
10%  of  silicious  concentrate,  assaying  3.97  oz.  gold.  The  final 
tailing  from  the  above  operation  assayed  0.52  oz.  gold,  showing 
an  extraction  by  concentration  of  80%.  The  extraction  by  canvas 
alone  was  13%,  showing  the  marked  adaptability  of  canvas  to  ore 
of  this  character  containing  so  much  extremely  fine  sulphide. 
Cyanide  treatment  of  the  slime  resulting  from  this  series  of  suc- 
cessive reductions  and  concentrations  reduced  the  tailing  to  0.22 
oz.  gold,  making  the  total  extraction  93  per  cent. 

This  method  was  adopted  because  the  required  plant  could 
be  conveniently  added  to  the  mill  already  installed,  and  the  same 
system  of  crushing  used.  Though  a  little  complicated,  the  process 
was  the  least  so  of  any  of  the  methods  considered.  The  high  cost 
of  fuel  and  supplies  in  Goldfield  barred  roasting.  Besides,  so  long 
as  the  ore  concentrated  well,  the  advantage  gained  by  segregating 
the  roastable  portion  of  the  ore  in  small  bulk  was  obvious. 

The  concentrate  from  the  sulphide  ore  is  now  being  shipped. 
It  may  later  be  treated  by  chlorination  on  the  ground.  The 
concentrate  from  the  oxidized  ore  is  about  to  be  treated  in  the  mill 
by  fine  grinding  and  prolonged  cyanidation. 

\ 

II.       THE    MILL 

In  considering  a  mill  for  the  combination  mine,  it  was  thought 
that  the  size  of  the  property  would  hardly  justify  the  initial  in- 
stallation of  more  than  10  stamps.  The  plant,  as  completed, 
is  unusually  large  for  such  small  capacity.  An  extensive  and 


ORE  TREATMENT  AT  THE  COMBINATION  MINE,    141 

costly  equipment  was  made  necessary  by  the  elaborate  process 
required  for  the  best  recovery,  and  by  the  decision  of  the  manage- 
ment to  reserve  one-half  of  the  mill  for  the  treatment  of  custom 
ore.  The  latter  required  one  complete  and  separate  unit;  thus  the 
whole  plant  was  spread  over  a  greater  area  than  would  otherwise 
have  been  necessary.  The  outlay,  however,  has  been  amply  justi- 
fied by  the  efficiency  of  the  machinery,  and  the  high  recovery 
obtained. 

The  lack  of  grade  for  millsite  introduced  several  problems 
into  the  construction  which  have  necessarily  affected  the  cost  of 
treatment,  namely,  the  elevating  of  ore  to  the  bins,  and  the  elevat- 
ing of  pulp  to  classifiers.  The  water  problem,  however,  was 
solved  at  the  start.  The  water  is  obtained  from  springs  situated 
about  ten  miles  west  of  the  mine,  and  is  pumped  to  the  mill  against 
a  head  of  about  800  ft.  at  a  cost  of  0.  Ic.  per  gal.  It  is  hot  as  it  comes 
to  the  surface  and  carries  about  0.1%  sodium  sulphate  and  a  trace 
of  sodium  chloride.  Though  slightly  brackish,  the  water  is  potable ; 
and  for  milling  purposes  the  sodium  sulphate  is  beneficial  in  assist- 
ing the  settlement  of  the  slime. 

The  ore  is  trammed  from  the  shaft  to  storage  bins,  from  which 
it  is  delivered  to  a  platform  above  a  10  by  16  Sturtevant  roll-jaw 
crusher,  where  it  is  mixed  with  the  required  amount  of  lime,  vary- 
ing from  5  to  10  Ib.  per  ton.  The  crusher  reduces  the  ore  to  about 
one-half  inch  size.  The  lack  of  fall  made  the  interposition  of  a 
sorting  grizzly  impossible.  Everything  passes  to  the  crusher 
and  is  delivered  direct  to  a  12-in.  belt-conveyor  set  at  an  angle  of 
20°,  which  elevates  the  ore  to  the  mill-bins.  There  are  four  of 
these  bins  for  the  four  units  of  five  stamps  each.  (Ten  more 
stamps  have  recently  been  added  for  treating  sulphide  ore.) 
The  point  of  discharge  at  the  top  of  the  mill  is  shifted  by  means  of 
the  usual  form  of  adjustable  carriage.  The  ore  is  fed  from  hanging 
feeders,  attached  to  the  bins,  into  the  low  mortars  of  the  Boss 
cantilever  battery  system.  This  type  of  battery  frame  and  mor- 
tar was  described  in  the  MINING  AND  SCIENTIFIC  PRESS,  of  Feb- 
ruary 17,  1906. 

In  the  following  description  of  the  milling  system,  I  shall 
first  take  up  the  treatment  of  the  oxidized  ore,  which  is  carried 
on  by  the  original  ten  stamps  and  cyanide  annex.  As  already 
explained,  the  mill  was  divided  into  two  separate  units  for  the 
purpose  of  treating  custom  ore.  Very  little  custom  ore,  however, 


142 


RECENT  CYANIDE  PRACTICE. 


has  been  received;  and  recent  favorable  developments  in  the  mine 
have  decided  the  management  to  devote  the  entire  mill  to  their 
own  ore.  In  the  following  account,  a  complete  five-stamp  system 
will  be  considered.  The  scheme  of  treatment  is  exhibited  diagra- 
matically  in  Fig.  12. 

Inside   amalgamation  is   carried   on  by   means   of  a   curved 
plate  screwed  to  the   chuck-block.     The   ore  is  crushed  through 


/0-/JSO£S  3X//HAS 


Fig.   12.     Treatment  of  Oxidized  Ore.    f  [ 


12-mesh  wire-screen.  Outside  the  screen  a  splash-plate  is  used. 
From  this  plate  the  pulp  falls  to  a  lip-plate  about  12  in.  wide, 
with  the  front  edge  slightly  bent  down,  giving  the  pulp  a  gentle 
drop  to  the  apron -plate.  There  are  three  plates  to  each  mortar, 
arranged  in  steps,  giving  an  amalgamating  surface  53  in.  wide  and 
about  12J  ft.  long.  The  whole  tray,  by  means  of  wheels  and  track, 
can  be  shifted  during  the  clean-up  of  the  battery,  as  shown  in 
Fig.  13  and  14. 


ORE  TREATMENT  AT  THE  COMBINATION  MINE.   143 

At  the  bottom  of  each  tray  is  a  small  cone  hydraulic  classifier, 
which  separates  the  coarse  mill-pulp  into  two  products:  (1)  Fine 
sand  and  slime,  which  passes  to  the  outer  discharge  lip  of  the 
Bryan  mill  and  thence  direct  to  the  concentrators;  (2)  coarse  sand, 
which  passes  to  the  Bryan  mill  for  re-grinding. 

The  ore,  being  extremely  hard  and  tough,  is  crushed  with 
1,350-ib.  stamps,  falling  100  times  per  minute,  with  a  6-in.  drop.  In 
spite  of  this,  however,  the  stamp-duty  is  only  3^  tons,  using  a  12- 
mesh  screen.  One  of  the  5-ft.  Bryan  mills,  running  at  half  speed, 
takes  all  the  coarse  sand,  from  10  stamps  (approximately  20  tons  per 
day),  and  crushes  it  through  a  No.  9  slotted  screen,  equivalent 


Fig.    13.     Cross-Section  of  Amalgamation  Table. 

to  40  mesh.  The  final  product  from  the  Bryan  is  passed  over 
two  6-ft.  Frue  vanners  and  two  6-ft.  Triumph  tables.  From  these 
concentrators  the  pulp  is  raised  by  two  54-in.  Fremier  sand-pumps 
to  two  sets  of  cone  classifiers.  This  system  is  a  modification  of 
that  introduced  by  Mr.  Merrill  at  the  Homestake  cyanide  plants. 
The  top  cone  takes  the  intermittent  discharge  from  the  sand-pump 
and  is  so  adjusted  by  valves  that  it  sends  a  fairly  uniform  flow  of 
pulp  to  the  two  smaller  cones.  The  top  cone  is  not  a  classifier. 
The  first  rough  classification  is  made  in  the  small  hydraulic 
cones,  from  which  a  stream  of  sand  flows  direct  to  the  sand 
vats.  The  overflow  from  these  small  cones,  consisting  of  slime 
and  fine  sand,  flows  to  the  larger  lower  cone,  where  a  closer  clas- 


ORE  TREATMENT  AT  THE  COMBINATION  MINE.    145 

sification  is  made.  The  stream  from  the  bottom  of  the  latter  also 
flows  to  the  leaching  vats.  The  overflow  from  this  large  lower 
•cone  passes  to  the  slime  settlers. 

The  pulp  from  the  Bryan  mill  may,  therefore,  be  said  to  con- 
sist of  two  products,  namely: 

{  Retained  on  100  mesh 41% 

1.  Sand    \  Passing  100,  retained  on  200 35%  •  67%  of  total. 

I  Passing  200  mesh 24%  . 

2.  Slime. .  .  Passing  200  mesh 90%  .  .  33%  of  total. 

This  is  not  considered  an  ideal  separation,  inasmuch  as  the 
slime  carries  a  large  amount  of  fine  sand.  In  spite  of  this,  however, 
the  recovery  from  the  slime  has  been  very  good  (over  95%)  since 
the  introduction  of  the  Butters-Cassel  filter.  A  contemplated 
re-arrangement  of  the  cones  is  expected  to  improve  the  extraction 
from  slime. 

In  a  small  mill,  classification  requires  constant  attention. 
Slight  interruptions,  the  suspension  of  one  battery  unit,  or  any 
variation  from  normal  operating  conditions,  at  once  affect  the 
flow  of  pulp  in  the  classifiers,  which  are  dependent  upon  nice 
adjustment  for  their  efficiency.  Obviously,  the  larger  the  mill,  the 
smoother  will  be  the  operation  of  this  system,  and  the  less  attention 
will  it  require. 

From  the  cones,  the  sand  flows  to  a  pipe  distributer  and  thence 
to  a  settling  vat,  of  which  there  are  four  on  each  side  of  the  mill. 
The  fourth  vat  was  added  after  the  completion  of  the  mill.  These 
vats  were  at  first  provided  with  an  overflow  lip  and  a  circular  launder 
to  carry  off  the  surplus  water.  It  was  found,  however,  that  occa- 
sional irregularities  in  classification  resulted  in  the  settlement 
of  slime  in  these  vats,  which  interfered  with  percolation.  The 
settlers  were  then  fitted  with  slime-gates,  and  the  overflow  from 
the  sand-settlers,  carrying  a  certain  amount  of  slime,  now  runs 
to  a  centrifugal  pump  at  the  lower  end  of  the  mill,  to  be  sent  to 
the  slime-settlers  for  clarification.  This  is  an  awkward  arrange- 
ment, but  was  unavoidable  owing  to  the  small  gradient  of  the 
millsite . 

When  the  sand-settler  is  filled,  the  surplus  moisture  is  removed 
by  a  Gould  vacuum  pump,  and  the  charge  shoveled  to  the  treat- 
ment vat  below.  Here  the  charge  is  given  an  eight  days'  treat- 
ment with  a  0.1%  and  a  0.2%  cyanide  solution,  and  the  residue 
discharged  by  sluicing  through  a  central  bottom-discharge  door. 


146  RECENT  CYANIDE  PRACTICE. 

The  slime  is  delivered  to  the  centre  of  a  conical-bottom  settler, 
provided  with  a  rim  overflow.  There  are  two  of  these  settlers 
on  each  side  of  the  mill.  Each  is  alternately  allowed  to  fill  and 
overflow  for  12  hours,  and  allowed  12  hours  for  settling.  A  pipe 
decanter  carries  off  the  surplus  water,  leaving  the  slime  with  about 
50%  moisture.  Sufficient  strong  cyanide  solution  is  added  to 
the  charge  of  slime  to  make  a  solution  of  from  0.15  to  0.2%  cyanide  ^ 
and  to  give  the  pulp  a  consistence  of  three  parts  solution  to  one 
of  slime.  By  means  of  a  centrifugal  pump,  the  pulp  is  transferred 
to  an  agitatior,  with  a  steep  cone -bottom.  By  means  of  valves,  the 
same  machine  (a  3-in.  Krogh  slime-pump)  is  applied  to  the  agita- 
tion, taking  the  slime  from  the  bottom  of  the  vat  and  throwing 
it  back  at  the  top.  A  supplementary  agitation  is  given  by  means 
of  a  mechanical  stirrer  revolving  slowly.  The  pulp  and  stirrer 
give  an  ideal  agitation,  being  sufficiently  complete  for  the  best 
results.  The  pump,  which  has  a  lift  of  about  10.  ft.,  is  run  at 
375  rev.  per  min.  Thus,  at  short  intervals,  the  whole  content 
of  the  vat  passes  through  the  pump,  where  it  is  aerated  by  means 
of  a  pet-cock  on  the  suction  pipe.  The  stirrer  prevents  the  settle- 
ment of  fine  sand  at  the  junction  of  the  cone  bottom  with  the 
staves,  and  keeps  up  the  agitation  during  pump  repairs.  The 
only  repair  required  in  the  pump  is  the  replacement  of  the  shaft 
about  once  per  month.  The  objection  urged  against  the  centrif- 
ugal pump  as  an  agitator — that  it  is  apt  to  clog  with  slime  during 
stoppages — is  not  a  sound  one.  The  'slime'  product  at  the  Com- 
bination mill  carries  a  large  amount  of  fine  sand,  and  the  pump 
has  repeatedly  been  started  up  after  stoppages  of  several  hours  „ 
without  the  least  trouble. 

After  agitation,  lasting  from  12  to  18  hours,  the  pulp  is  dis- 
charged into  a  slime  reservoir,  a  vat  of  large  capacity  provided 
with  a  mechanical  stirrer  from  which  it  is  drawn,  as  required, 
for  filtration  in  the  Butters-Cassel  filter. 

A  filter-press  was  at  first  used  for  filtering  the  slime.  This, 
was  an  American  machine  consisting  of  fifty  42-in.  plates  and 
2-in.  distance  frames,  and  had  a  capacity  of  2J  tons  of  (dry) 
slime.  It  was  evidently  made  of  poor  material,  as  it  was  the  source 
of  exasperating  trouble  through  breakage.  The  plates  were 
continually  cracking  under  a  pressure  much  below  the  guaranteed 
maximum,  and  the  outlet-cocks  getting  out  of  order  or  breaking. 
Moreover,  the  operation  of  pressing,  washing,  and  discharging; 


ORE  TREATMENT  AT  THE  COMBINATION  MINE.   147 

was  extremely  slow,  requiring  about  five  hours,  and  the  operating 
expense  high,  requiring  two  men  on  each  of  the  three  shifts  at 
the  prevailing  laborer's  wage  of  $4  per  day,  to  say  nothing  of  the 
cost  of  the  filter-cloths.  It  is  fair  to  suppose  that  one  of  the  high- 
class  foreign  presses  of  the  Dehne  type  might  have  given  better 
satisfaction.  At  best,  however,  filter-pressing  is  not  to  be  com- 
pared with  ^he  system  now  in  use,  especially  as  regards  cost  of 
operating,  and  the  completeness  of  the  washing  operation. 

The  essential  points  of  difference  between  the  Butters-modifi- 
cation of  the  Cassel  filter  and  the  other  vacuum-filtering  schemes 
are  the  extreme  simplicity  in  the  design  of  the  filter-leaf  or  frame, 
and  the  fact  that  these  frames,  throughout  the  operation,  are  al- 
ways stationary.  In  the  Combination  plant  there  are  28  frames 
(5  by  10  ft,.)  set  4J  in.  apart  in  a  box  10  ft.  square  with  a  pointed 
bottom  inclined  at  an  angle  of  50°.  The  slime -pulp  is  introduced 
at  the  point  of  the  box,  and  a  vacuum  of  22  in.  of  mercury  is 
maintained  for  about  20  min.,  during  which  time  a  cake  is  deposited 
on  each  side  of  the  frame  f  to  1  in.  thick.  The  surplus  pulp  is 
then  withdrawn  to  the  slime  reservoir  and  the  wash  introduced, 
consisting  of  a  weak  solution  of  cyanide.  When  the  cakes  are 
thoroughly  washed,  the  weak  solution  is  withdrawn  into  its  proper 
vat,  and  water  introduced,  until  the  frames  are  completely  im- 
mersed. The  object  of  this  final  water  is  to  assist  in  removing 
the  cakes.  More  water  is  introduced  into  the  interior  of  the  frames 
under  a  low  head.  This  causes  the  cakes  to  drop  off  clean,  into 
the  pointed  bottom  of  the  filter-box,  whence  they  are  finally 
removed  by  sluicing.  The  whole  operation  requires  about  3J 
hours,  and  about  nine  tons  (dry)  slime  are  treated  at  each  charge. 
The  plant,  therefore,  has  a  capacity  of  about  63  tons  per  day. 
It  is  operated  by  one  man  on  each  shift.  The  principal  power 
required  is  for  pumping  the  pulp  and  the  various  solutions  in 
and  out  of  the  filter-box,  and  for  operating  the  vacuum  pump. 
In  addition,  the  gold-bearing  solution  discharged  from  the  vacuum 
pump  is  raised  about  30  ft.  and  forced  through  the  discarded 
filter-press  now  used  for  clarifying  purposes.  The  whole  consumes 
about  10  h.p.  A  15-h.p.  motor  has  been  installed  for  this  work, 
but  has  extra  work  to  do  not  connected  immediately  with  filtering. 

The  filter-plant  has  required  no  repairs  since  it  was  first 
operated  in  February  of  this  year,  and  has  worked  in  the  most  satis- 
factory manner.  The  cost  of  filtering  (exclusive  of  power)  has 


148  RECENT  CYANIDE  PRACTICE. 

been  reduced  from  96c.  per  ton  of  slime  in  January  (using  filter- 
press)  to  26c.  in  May  (using  the  Butters  system).  The  power 
consumption  appears  to  be  about  the  same  in  the  two  processes. 
Treatment  of  Sulphide  Ore. — This  ore  is  crushed  to  12  mesh, 
in  two  five -stamp  batteries,  and  run  over  plates  to  take  up  the 
small  quantity  of  free  gold  present.  See  Fig.  15.  A  classifier  at 
the  end  of  the  plate-tray  removes  the  coarse  sand  and  sulphide, 
which  go  to  a  Wilfley  concentrator;  the  overflow  of  slime  and  fine 
sand  passing  to  the  outer  lip  of  a  Bryan  mill.  One  Wilfley  table, 
therefore,  removes  the  coarse  sulphide  from  the  product  of  ten 
stamps  crushing  to  12  mesh.  The  tailing  from  the  Wilfley  is 
raised  in  a  bucket-elevator  to  a  Bryan  mill,  which  crushes  it  to 
40  mesh  (No.  9  slotted  screen).  The  tailing  from  the  Bryan 


>i 


UJ 

I  ig.    15.     Treatment  of  Sulphide  Ore. 

mill  joins  the  stream  of  slime  from  the  small  classifier  and  passes 
to  four  6-ft.  Frue  vanners.  Here  a  large  quantity  of  fine  sulphide 
is  removed.  The  Frue  tailing  is  then  elevated  by  a  sand-pump 
to  a  classifier  above  a  4  by  12  ft.  Abbe  tube-mill  of  the  trunnion 
type.  The  cone  acts  as  a  classifier  as  well  as  a  de-watering  de- 
vice. The  coarse  sand  passes  to  the  tube-mill;  the  slime  overflow 
joins  the  tailing  from  the  tube-mill  and  goes  to  three  Wilfley 
slime-tables  of  the  latest  pattern.  The  tailing  from  the  last, 
consisting  of  slime  and  fine  sand,  is  elevated  to  the  cone -classifier 
in  the  original  mill,  where  it  is  mixed  with  the  oxidized  tailing 
and  treated  in  the  cyanide  plant. 

This  plant  was  only  operated  a  few  days,  and  then  shut  down, 
pending  the  installation  of  two  Wilfley  slime-tables,  making  three 
in  all,  the  first  having  been  set  up  experimentally.  During  this 


ORE  TREATMENT  AT  THE  COMBINATION  MINE.     149 

short  run  the  results  were  very  promising.  Of  the  final  product 
from  the  slime-table,  87%  passed  through  200  mesh,  and  the  three 
stages  of  reduction  showed  a  saving  by  concentration  of  over 
80%  of  the  contained  gold.  With  the  cyanide  treatment  of  the 
slime  tailing,  a  confirmation  of  the  small  mill-run  is  expected, 
namely,  better  than  90%  recovery. 

It  is  too  soon  to  give  the  results  of  tube-mill  work.  The  mill 
is  lined  with  2^-in.  silex  blocks,  which  will  be  replaced  by  blocks 
4  in.  thick. 


Fig.   16.     Tube-Mill  and  Wilfley  Slime-Tables. 

Precipitation  is  accomplished  in  the  usual  way  by  means 
of  zinc  shaving.  The  solutions  are  richer  than  are  usually  seen  in 
cyanide  mills,  reaching  as  high  as  one  ounce  per  ton  in  gold. 
Owing  to  the  absence  of  silver,  which  undoubtedly  facilitates  the 
precipitation  of  gold,  a  very  large  zinc  surface  is  required.  The 
precipitate  is  refined  with  sulphuric  acid  and  smelted  in  a  pot- 
furnace,  with  gasoline,  a  powerful  jet  being  maintained  by  means 
of  a  small  upright  Leyner  compressor. 


150 


RECENT  CYANIDE  PRACTICE. 


The  following  details  of  costs  for  milling  and  cyaniding  in- 
dicate a  few  of  the  difficulties  met  with  in  an  isolated  district 
where  the  cost  of  supplies,  and  of  labor,  power,  and  water  are 
unusually  high.  And  then  it  must  be  borne  in  mind  that  the  mill 
is  of  small  capacity.  The  change  from  steam  to  electric  power— 
the  latter  being  furnished  by  a  local  concern  operating  a  90-mile 
transmission  line — reduced  the  cost  of  power  from  a  maximum 


Fig.   17.     Slime-Agitation  Vat. 


of  $1.73  per  ton  (January  1906)  to  $0.76  (May,  1906).  We  have 
already  noted  the  great  reduction  in  cost  effected  by'  introducing 
a  new  filtering  system  for  slime.  The  marked  decrease  in  opera- 
ting expense  during  February  was  due  to  increasing  the  capacity 
of  the  mill  by  annexing  10  stamps,  making  20  in  all.  While 


ORE  TREATMENT  AT  THE  COMBINATION  MINE.  151 

the  total  milling  and  cyaniding  cost  of  $5.828  per  ton  seems  high, 
it  is  really  not  so  when  local  conditions  are  considered.  It  is 
expected  that  further  retrenchment  will  soon  cut  this  down  to 
$5  per  ton. 

The  recovery  in  the  mill  and  cyanide  plant  has  attained  a 
maximum  of  93%  for  several  consecutive  months,  and  has  averaged 
over  90  per  cent. 


1 

i 

o 

1 

0 

5 

1 

SUPPLIES. 

total  cost  
Fotal  supplies  

•«?  iO  C^J  CNI  O 

OOOOO 

NOTE—  The  average  consumption  of  chemicals  in  treatment  of  sand  and  slime  during  1906  has  been  as  follows:  Cyanide,  1.27  Ib.;  zinc  0.6  Ib.;  and  lime,  11  pounds. 

MILLING  AND  CYANIDING  COSTS  PER  TON  OF  ORE  MILLED  (1906). 

lotal  costs  

OOt--^H  CMOO 
CO  »—  (  CM  CM  CM 
CM  OO  OS  (MOO 

—    --   •-  I  -  ..- 

8 

Total 
per 
ton. 

Supplies  .  .  . 

£COCOCO*i 

Labor  

•«f  CO  CO  CO  CO 

Miscellaneous  

jlSsS 

-0000 

ooooo 

Other  chemicals  

:§§  :g 
•  od    -d 

Maintenance 
and 
repairs. 

Supplies  .  .  . 

Labor  

ooooo 

Filter  cloths  

5OCO       •      •       • 

00     •     ;     ; 

Lighting  

llSi  ; 

0000     - 

Lime  

IOIOIOI—.-H 
lO  »O  .-1  1C  r-< 
rH  »—  1  t-H  T—  *  CO 

odddo 

Tools 

ooooo 

Lubricating  

ooooo 
ooood 

§333 

ooooo 

Acid  

Assaying 
and 
sampling. 

Supplies  .  .  . 

Zinc  

CM  t-lOlOlO 

1-1  O  O  O  "-i 

ooooo 

Labor  

OD  r~  OO  CM  C4 

t~-  00  CO  CO  ^< 
CO  CM  CM  CO  CO 

odddd 

Cyaniding  

Supplies  .  .  . 

ooddd 

Cyanide  

odddo 

'  Labor  

M  i-i  i-i  I-H  d 

LABOR. 

Total  labor  

iisi| 

Concentrating  

doddd 

Stamping 
and 
amalgamating. 

Supplies  .  .  . 

doddd 

Butters  flime-filter.  .  .  . 

:0odo 

Labor  

ooooo 

fl  CM  CM  CM  CM 
00000° 

Crushing  and  elev 

it  ing 

Tailing  dam  

:odoo 
odddo 

Water  and  pumping  

Shovelers  

Heating  

O^  O5     •     • 

od    •    •    • 

Power  

•*CO^-l»OCO 
^-i^-ir-HOO 

Filter-press  

10  on    •    •    • 
o'd     •     ;     ; 

Mill  superintendent  

Solution  men  

sills 

odddd 

Ore  tons. 

«OOOiO"3 

Oi  •**<  ^H  O  ^t< 

Ore  tons. 

COOO'O'O 

sisjti 

s 

Q 

i 

ifc 

FILTER  MACHINES 

(October  13,  1906) 

The  Editor: 

Sir — In  view  of  the  scarcity  of  literature  touching  the  Moore 
and  Butters  processes,  some  comment  on  Mr.  R.  Oilman  Brown's 
recent  papers  may  be  of  interest. 

The  process  at  Bodie  differs  from  that  at  Telluride  (as  described 
in  The  Engineering  and  Mining  Journal,  July  7,  1906)  in  a  notable 
point,  the  cake  being  blown  off  by  air  into  a  hopper  instead  of  by 
water  into  the  wash-vat.  The  latter  method  is  distinctly  advan- 
tageous as  the  strain  on  the  niters  is  considerable,  while  air  quickly 
enlarges  leaks.  Further,  a  stoppage  of  a  few  minutes  caused,  for 
example,  by  a  circuit -breaker  being  thrown  out,  will  cause  a  con- 
siderable portion  of  the  cake  to  drop  into  the  wash- vat,  which 
is  both  inconvenient  and  expensive,  unless  the  vat  is  designed  for 
pulp  discharge.  The  photograph  given  by  Mr.  Brown  shows  that 
the  baskets  are  likely  to  hang  so  unevenly  that  to  use  water, 
the  basket  being  hung  up,  would  consume  much  time  or  give  a 
faulty  discharge  at  the  high  end.  The  discharge  of  cake  by  water 
when  the  basket  is  immersed,  is  perfect,  while  discharge  by  air 
entails  scraping  at  the  edges.  A  great  disadvantage  of  moving 
baskets  is  that  an  accident  to  the  somewhat  complex  moving  gear 
puts  more  than  one  basket  out  of  commission,  while,  if  the  pulleys 
of  the  hoisting  chains  wear  far,  there  is  a  chance  of  an  awkward 
accident  through  a  chain  slipping  one  or  more  links.  The  ability 
to  raise  the  baskets,  however,  facilitates  replacing  leaky  filters. 
In  the  Butters  process  it  is  to  be  expected  that  the  unmoved 
filters  will  outlast  those  raised  and  air-distended;  but  besides 
this  we  have  an  economy  in  labor.  To  raise  and  discharge  a  basket 
takes  half  an  hour  and  the  basket-man's  whole  attention,  while 
in  the  Butters  process  his  duty  is  mainly  to  turn  the  valves.  With 
the  charging  and  washing  intervals  given  by  Mr.  Brown,  two  bas- 
kets would  keep  a  man  busy,  while  he  would  be  badly  overworked 
with  quick  charges  like  those  obtained  by  Mr.  Lamb  on  Goldfield 
ore. 

H.  W.  GARTRELL. 

Bisbee,  Arizona,  September  7. 


WHAT  IS  SLIME? 

(October  20,  1906) 

The  Editor: 

Sir — Slime  is  now  receiving  so  much  attention  and  is  so  con- 
spicuous a  feature  in  ore  treatment  that  there  seems  to  be  a  grow- 
ing disposition  to  designate  some  measure  of  fineness  which  shall 
define  it  and  receive  general  recognition. 

We  know  slime  now  as  a  condition  of  pulp  that  requires 
attention  more  or  less  different  from  that  given  to  sand.  In  my 
own  experience  I  have  found  that  slime,  as  it  appears  to  us,  is 
not  altogether  a  matter  of  extreme  fineness,  but  the  manner  of 
creating  it  is  also  a  factor.  Aeration  in  process  of  crushing  greatly 
increases  the  visual  evidence  of  slime. 

Many  years  ago  I  had  been  crushing  an  ore  with  stamps, 
using  but  little  water,  and  the  pulp  went  largely  to  slime,  although 
a  medium  screen  was  used.  Near-by  a  large  slow-traveling 
Chilean  mill  was  installed  and  began  crushing  on  the  same  ore. 
Instead  of  screens  they  used  float  overflow,  about  18  in.  above 
the  die.  To  my  surprise,  there  was  no  evidence  of  slime  in  the 
vat  which  received  the  pulp,  the  water  flowing  away  from  it  clear. 
In  this  case  there  was  no  possible  contact  of  air  with  the  pulp  at, 
or  after,  its  crushing,  as  the  stream  had  but  a  gentle  flow  (without 
falling)  from  the  mill  to  the  tank.  For  concentration,  it  is  plain 
that  aeration  of  pulp  is  not  desirable. 

M.  P.  Boss. 

San  Francisco,  October  5. 


THE  ACTION  OF  OXYGEN  IN  CYANIDE 

SOLUTIONS 

BY  H.  JULIAN 

(October  27,  1906) 

*A  doubt  has  for  some  time  existed  as  to  the  accuracy  of  the 
generally  accepted  idea  that  free  oxygen  is  primarily  essential 
for  the  dissolution  of  gold  in  cyanide  solutions,  according  to  the 
equation : 

4KCy  +  2Au  +  O  +  H2O  =  2KAuCy2  +  2KOH. 

Experiments  are  described  which  go  to  show  (1)  that  free 
oxygen  plays  no  primary  part  in  the  reaction,  (2)  that  any  assis- 
tance given  by  free  oxygen  is  of  a  secondary  nature,  and  (3)  that 
free  oxygen  exerts  a  retarding  influence. 

The  experiments  show  that  the  galvanometer  points  to  the 
presence  of  free  oxygen  as  having  a  retarding  influence  on  the 
dissolution  of  the  gold,  whereas  the  balance  points  to  it  being  of 
material  assistance.  The  cause  of  the  two  instruments  not  agree- 
ing is  discussed,  and  is  attributed  to  the  formation  of  local  voltaic 
circuits.  These,  in  the  first  instance,  deposit  hydrogen  and  oxy- 
gen, which  it  may  be  assumed,  become  occluded  at  their  respec- 
tive electrodes  until  the  systems  are  in  equilibrium.  It  is  pointed 
out  that  the  cyanogen  leaves  the  solution  to  combine  with  the 
gold  rather  than  that  gold  particles  pass  into  the  solution,  and 
it  is  shown  that  cyanogen  does  not  leave  the  solution  until  the 
deposited  oxygen  has  been  occluded  to  a  certain  degree  of  con- 
centration. The  reason  for  this  is  that  the  expenditure  of  energy 
necessary  to  remove  oxygen  from  the  solution  is  less  than  that 
necessary  to  remove  cyanogen;  but  when  oxygen  is  occluded  to 
a  certain  concentration,  the  expenditure  of  energy  then  necessary 
to  cause  the  metal  to  occlude  a  further  amount  becomes  as  great 
as  that  necessary  to  begin  to  remove  cyanogen  from  the  solution. 
The  available  energy  is  obtained  from  the  metal  and  solution, 
and  it  follows  that  when  the  solution  is  very  dilute  the  available 
energy  is  too  small  to  remove  cyanogen,  oxygen  being  then  alone 


*Abstract  from  British  Association  Report,  prepared  by  the  author  and  published  in  the 
Journal  of  the  Chemical,  Metallurgical  and  Mining  Society  of  South  Africa. 


156  RECENT  CYANIDE  PRACTICE. 

deposited.  From  this  it  may  be  conjectured  that  no  metal  actually 
combines  with  cyanogen  until  the  solution  has  a  certain  mini- 
mum strength. 

The  presence  of  dissolved  oxygen  in  the  solution  has  a  sec- 
ondary effect  in  the  process  of  dissolution,  by  oxidizing  the  occluded 
hydrogen  produced  through  the  action  in  the  local  voltaic  cir- 
cuits. This  results  in  upsetting  the  equilibrium,  and  introducing 
into  the  circuits  concentration  gas  cells,  which  soon  bring  about 
equilibrium  again,  but  this  time  with  oxygen  at  both  electrodes 
at  different  concentrations,  instead  of  hydrogen  and  oxygen.  If, 
now,  excess  of  dissolved  oxygen  diffuses  to  either  of  the  electrodes 
the  equilibrium  is  again  upset,  and  an  E.M.F.  is  generated  by  the 
gas  cell  in  opposition  to  the  E.M.F.  generated  by  the  metal  couple; 
the  net  result  being,  of  course,  a  current  in  the  direction  of  the 
greater  E.M.F.  As  the  strength  of  the  solution  increases  after 
a  certain  point,  the  E.M.F.  due  to  the  metal  couple  increases 
rapidly,  whereas  that  due  to  the  oxygen-concentration  cell  remains 
constant  or  increases  only  slowly. 

The  increase  in  the  E.M.F.  of  the  metal  couple  appears  to 
be  largely  due  to  the  formation  of  AuCy,  a  compound  having  a 
high  potential,  which  acts  as  an  electrode.  This  deposits  in  films, 
varying  in  density  or  thickness  to  a  maximum  with  the  strength 
of  the  solution.  A  couple  results  of  Au-AuCN.  After  this  stage 
of  the  process,  when  AuCy  is  formed,  oxygen  ceases  to  exert  an 
influence.  That  is  to  say,  the  metal  passes  into  solution  by  the 
AuCy  dissolving  in  the  potassium  cyanide  solution,  as  one  salt 
dissolves  in  the  solution  of  another. 

The  effect  of  the  gas  cell  is  best  observed  in  highly  dilute 
solutions  at  ordinary  or  low  temperatures.  After  a  certain  strength 
is  attained,  dependent  on  temperature,  the  effect  of  the  gas  cell 
is  entirely  masked.  At  the  higher  temperatures  the  E.M.F.  of 
the  gas  cell  diminishes,  with  a  corresponding  increase  in  the  E. 
M.F.  of  the  Au-AuCy  couple.  At  boiling  point  the  retarding 
oxygen  effect  of  the  gas  cell  on  the  dissolution  of  the  metal  prac- 
tically disappears. 


SOME  TAILING  SAMPLERS 
BY  R.  OILMAN  BROWN 

(November  3,  1906) 

It  is  hardly  too  much  to  say  that  of  tailing  samplers  there 
should  be  no  end,  and  the  description  of  good  devices  of  this  class 
at  least  serves  the  laudable  end  of  removing  the  underpinning 


Fig  18.    Tailing  Sampler  in  Use  at  the  Ymir  Mill,  B.  C. 

from  those  who  still  evade  the  use  of  such  devices.     It  can  not 
but  be  remarkable  that,  even  at  this  late  day  when  so  much  has 


158  RECENT  CYANIDE  PRACTICE. 

been  written  of  the  need  of  a  systematic  check  on  milling  work, 
it  should  be  rather  the  exception  to  find  automatic  samplers  in- 
stalled in  smaller  mills. 

It  is  not  the  every-day  mechanic  who  can  devise  a  machine 
which  at  regular  intervals  can  be  self-instigated  to  take  a  quick 
cut  through  a  stream  of  tailing,  and  many  of  the  devices  fur- 
nished by  manufacturers  are  open  to  objection  on  the  score  of  high 
cost,  limited  adaptability,  and  complicated  mechanism.  The 
two  illustrated  herewith  are  practical  machines,  which  have  been 
installed  by  home  talent  and  have  stood  the  test  of  long  operation. 

The  first,  illustrated  in  Fig.  1,  2,  and  3,  samples  the  tailing 
from  the  Ymir  mill,  in  British  Columbia.  It  can  be  described 
as  follows:  A  is  a  vertical  chute  down  which  the  tailing  flows, 
D  is  a  sampling  box  with  Vie'*11-  sl°t  suspended  by  the  hangers 
J  Jt,  which  are  free  to  swing.  From  the  spout  of  D  the  sample 
runs  into  the  receptacle  B\  the  apron  M  guards  against  splash, 
and  C,  with  its  inclined  cover,  further  protects  the  sample  from 
accidental  salting.  When  the  sampler  is  in  the  position  shown, 
the  tailing-stream  falls  into  the  hopper  K.  The  actuating  device 
is  shown  at  the  right  of  Fig.  1.  F  is  a  water  pipe  with  a  regulat- 
ing valve,  £  is  a  water  can  secured  eccentrically  on  a  crank-shaft  G 
and  held  vertical  by  an  adjustable  weight  H.  The  crank,  through 
its  connecting  rod  and  fork  /,  causes  D  to  swing  back  and  forth 
through  the  stream  of  tailing. 

The  operation  is  as  follows*  When  the  water  dripping  from 
F  has  reached  the  proper  point,  it  overbalances  the  counter- 
weight H,  and  E  turns  down  toward  the  left,  spills  its  water  into 
the  housing  L,  and  is  carried  around  by  its  inertia  to  its  original 
position,  raising  the  latch  N  as  it  passes  and  then  falling  back 
against  it.  By  adjustment  of  H,  this  can  be  made  to  happen 
with  little  jar.  It  is  easy  to  regulate  this  device  to  take  samples 
from  five-minute  intervals  up  to  30.  B  and  E  are  the  ordinary 
5-gal.  coal-oil  cans  of  commerce.  It  should  be  noted  that  in 
Fig.  3  the  actuating  device  has  been  omitted,  and  in  Fig.  2,  the 
apron  M.  The  other  device  is  installed  at  the  cyanide  plant 
of  the  same  company.  Here  A  (Fig.  4,  5,  6,)  is  the  tailing  chute 
and  the  sampling  box  B  is  suspended  in  the  same  way  as  before, 
with  the  exception  that  the  hanger  is  bent  from  a  single  piece 
of  iron;  this  construction  is  demanded  because  the  connecting 
rod  7  works  only  on  one  side.  The  actuating  device  is  a  flutter 


SOME  TAILING  SAMPLERS. 


159 


wheel  G  in  the  tailing-launder  driving  the  grooved  wheel  E  through 
the  medium  of  a  crossed  cord.  Hanging  loose  of  the  shaft  of  E 
is  a  heavy  arm  of  iron  C,  connected  by  7  to  the  sampling-box. 
The  pin  D  carries  C  around  with  E  until  it  reaches  the  position 
shown  in  Fig.  4.  From  this  position  C  falls  by  its  own  weight  to 
its  lower  position,  swinging  the  sample-box  through  the  stream. 
In  the  lower  position  it  remains  until  D  catches  up  with  it,  when 
it  is  carried  around  again  to  the  upper  position.  During  this 
movement  it  swings  B  back  still  further  out  of  the  stream.  This 
is  a  very  pretty  mechanical  arrangement  and  works  admirably. 


Fig.    19.     Another  Sampling  Device. 

The  use  of  the  nutter  wheel  is,  however,  open  to  objection  in  that 
the  time  interval  at  which  the  sample  is  taken  varies  somewhat 
with  the  quantity  of  pulp  passing.  Assume  that  half  the  mill 
is  hung  up;  if  under  this  condition  the  wheel  G  revolves  half  as 
fast,  the  sample  interval  will  be  doubled,  anct  as  there  is  but  half 
as  much  tailing  dropping  from  A,  the  amount  of  sample  taken 
for  this  period  will  be  one-quarter  of  normal,  when  to  give  true 
results  it  should  be  one-half.  With  half  the  flow,  no  doubt  the 
wheel  G  would  not  slow  down  to  the  same  extent,  but  it  would 


160  RECENT  CYANIDE  PRACTICE. 

slow  down  slightly,  and  observation  of  the  sampler  in  operation 
shows  this  to  be  the  case.  Moreover  under  the  best  of  conditions 
the  speed  of  G  is  not  uniform,  so  that  a  better  arrangement  would 
be  to  have  E  actuated  through  the  medium  of  some  reduction 
gearing  from  the  mill-shafting  or  from  a  water-wheel  driven  by  a 
stream  that  can  be  regulated. 


COPPER  IN  CYANIDE  SOLUTIONS 

(Novembers,  1906) 

The   Editor: 

Sir — I  note  what  C.  A.  Arents  says  about  copper  precipi- 
tating on  zinc  shaving,  and,  having  had  a  similar  experience,  I 
can  agree  with  him  that  copper  may  not  be  a  hindrance  to  good 
precipitation. 

Two  years  ago  I  was  operating  a  cyanide  plant  in  the  desert 
country,  treating  a  dump  of  old  pan-mill  tailing.  One  mill  had 
burned  down  there,  and  there  were  numerous  small  pieces  of 
burned  copper  plate  mixed  with  the  sand.  The  copper  did  not 
begin  to  show  until  the  plant  had  been  running  about  four  months. 
The  concentration  of  copper  in  the  solution  was  probably  due 
to  the  fact  that  no  wash-water  or  weak  solution  left  the  plant 
except  that  existing  in  the  residues  as  moisture. 

Copper  began  to  show  first  on  the  fresh  zinc  that  was  put 
in  the  lower  boxes  and  in  a  month  or  six  weeks  it  had  worked 
up  to  the  head  boxes.  I  was  somewhat  alarmed  at  first,  and 
tried  to  keep  it  off  by  adding  cyanide  to  the  filter-box.  The 
stronger  solution  would  take  it  off  in  a  few  hours  but  only  to  be 
back  again  the  next  morning.  I  took  daily  samples  (for  a  while) 
of  the  solution  leaving  the  boxes,  but  they  only  assayed  a  trace 
to  a  few  cents,  when  the  solution  entering  averaged  about  five 
dollars  per  ton. 

The  gold  seemed  to  precipitate  on  the  copper-covered  shav- 
ing so  that  there  were  shades  from  bright  copper,  bronze,  to  black. 
There  was  a) so  mercury  in  the  sand  which  was  taken  up  by  the 
solution  and  precipitated,  causing  some  of  the  shaving  to  look 
like  silver. 

The  value  of  the  precipitate  shipped  was  about  $16  per  Ib. 
before  the  copper  began  to  show,  and  gradually  it  decreased  to 
about  $8  per  Ib.  But  with  the  exception  of  making  a  lower  grade 
precipitate,  the  copper  did  no  harm  whatever,  and  the  precipita- 
tion was  as  good  after  as  before. 

E.  D.  CHANDLER. 

Rochford,  S.  D.,  October  17. 


TUBE-MILL  LINING 

(Novembers,  1906) 

The   Editor: 

Sir — In  your  issue  of  July  28,  1906,  I  read  with  pleasure 
the  article  on  Tube-Mill  Lining,'  in  which  the  Barry  honeycomb 
is  described  and  illustrated. 

There  is  no  doubt  that  this  patent  is  a  great  improvement 
on  the  silex  lining  which  the  Waihi  Co.  imported  with  their  tube- 


c 


Fig.  20.     A  Tube-Mill. 


mills.  Anyone  who  has  had  experience  with  the  silex  lining 
knows  how  expensive  and  troublesome  it  is  when  used  for  wet 
grinding,  and  consequently  will  welcome  any  improvement  in 
the  matter  of  initial  cost  and  maintenance.  The  ordinary  iron 
or  steel  liner,  with  smooth  inner  surface,  is  also  unsatisfactory, 
for,  owing  to  the  stones  sliding  and  thereby  becoming  flat,  much 
of  their  efficiency  for  grinding  is  lost. 


T.UBE-MILL  LINING. 

Having  run  tube-mills  for  some  considerable  time,  grinding 
the  sandy  portion  of  the  pulp  from  stamps,  crushing  hard  ore 
through  all  grades  of  wire-screen  from  30  mesh  down  to  10  mesh, 
and  having  had  trouble,  owing  to  the  use  of  smooth  iron  liners, 
I  set  to  work  and  brought  out  an  improved  iron  liner,  which 
consists  of  segments  of  a  special  hard  mixture  of  iron,  costing 
14s.  per  cwt.  (say,  three  cents  per  pound),  when  manufactured 
into  liners.  These  liners  are  4  ft.  long  and  1J  in.  thick,  and  are 
of  such  a  width  that  12  form  a  circle  of  4  ft.  diam.,  which  is  the 
diameter  of  the  tube-mill.  Instead  of  having  holes  cast  for  bolts, 
they  have  only  two  half  holes  on  each  long  edge.  Over  the 
junction  of  each  pair,  a  cast-iron  bar  2^  in.  square  is  placed  and 
bolted  by  two  square-headed  bolts  through  the  lining  and  outer 
shell  of  the  tube-mill.  Thus  there  are  12  cast-iron  bars  which 
run  longitudinally  through  the  mill,  and  the  effect  is  to  form  a 
casing  of  flint  stones  which  does  not  slip  and  which  protects  the 
iron  lining. 

Such  liners  have  been  used  for  some  time  in  the  mill  of  the 
Komato  Reefs  Co.,  New  Zealand,  and  have  lasted  for  18  months 
before  being  renewed.  Without  the  square  bars,  the  smooth 
iron  liners  only  last  six  to  eight  months. 

The  cost  of  liners  and  bars  for  a  4  by  16  ft.  tube-mill  is  £84, 
and  two  men  can  fix  them  all  in  position  in  three  shifts  of  eight 
hours  each;  the  total  cost  with  bolts  would  be,  say,  £90.  The 
amount  of  sand  passing  through  the  tube-mill  is  70  tons  per  day 
of  the  material  discharged  through  the  10-mesh  screen  of  the 
stamp-battery,  and  the  finished  product  has  the  fineness  that 
would  be  secured  by  the  use  of  a  35-mesh  screen  on  the  battery. 
Thus  the  cost  of  lining  is  about  seven-tenths  of  a  penny,  or  1.4  c. 
per  ton  of  sand  ground. 

S.  D.  McMiKEX. 

Komata,  New  Zealand,  September  2. 


COMPARATIVE  TESTS  BETWEEN  COKE  AND 
CRUDE  OIL  FOR  MELTING  PRECIPITATE 

(November  24,  1906) 

The  Editor: 

Sir — It  may  interest  your  readers  to  know  that  two  experi- 
ments were  made  at  the  Butters  Salvador  mines,  in  Salvador, 
to  determine  the  relative  efficiency  of  coke  and  crude  oil  in  melting 
precipitate  from  the  cyanide  plant;  the  first  was  on  the  ordinary 
San  Sebastian  clean-up  from  the  acid  refining  box,  and  the  other 
was  on  silver  precipitate  from  Divisadero.  The  costs  are  calcu- 
lated on  a  basis  of  coke  at  $0.0208  (gold)  per  lb.,  and  oil  at  $0.252 
(gold)  per  gal.  laid  down  at  San  Sebastian;  white  labor  at  $3  per 
shift  at  10  hours;  and  compressed  air  at  Ic.  per  hour. 


FIRST    TEST 


OIL. 


Sept.  11,  1906. 


Sept.  13,  1906. 


Precipitate 2,448  oz.  Troy       precipitate 1  991  oz.   Troy 

Oil 15.2  gal.  ' 


Time    1\    hr. 

Cost  of  fuel  per  oz.  of  pre- 
cipitate   $0.00156 

Cost  of  fuel  per  1,000  oz.  of 

precipitate 1 .  56 

Cost  of  white  labor  per  1,000 
oz.  of  precipitate 0.91 

Cost  of  air  per  1,000  oz.  of 
precipitate 0 . 03 


Total $2 . 50 

Balance  in  favor  of  oil  per 

1,000  oz.  of  precipitate  . .    1 . 06 


Total  . .  .  .  $3  . 56 


221  lb. 
8J   hr. 


Coke 

Time  ........................ 

Cost  of  fuel  per  oz.  of  pre- 

precipitate  .............  $0  .  00231 

Cost  of  fuel  per  1,000  oz.  of 

precipitate  .............    2.31 

Cost  of  white  labor  per  1,000 

oz.  of  precipitate  .......    1  .  25 


Total  . .  .  .  $3  . 56 


TESTS   BETWEEN  COKE  AND  OIL. 


165 


SECOND    TEST 


Total $1.50 

Balance  in  favor  of  oil  per 

1,000  oz.  of  precipitate .  .  .1 . 03 


OIL. 

Sept.  20,  1906. 

Precipitate 5,664  oz.  Troy   ! 

Oil 21  gal. 

Time    10J  hr. 

•Cost  of  fuel  per  oz.  of  pre- 
cipitate   $0 . 00093 

€ost  of  fuel  per  1,000  oz.  of 

precipitate 0 . 93 

€ost  of  white  labor  per  1,000 
oz.  of  precipitate 0 . 55 

•Cost  of  air  per  1,000  oz.  of 

precipitate 0 . 02 


Total $2 . 53 


COKE. 

Sept.  21,  1906. 

Precipitate 3,524  oz.  Troy 

Coke 283  Ib. 

Time    . 10J  hr. 

Cost  of  fuel  per  oz.  of  pre- 
cipitate  .$0.00167 

Cost  of  fuel  per  1,000  oz.  of 

precipitate 1 . 67 

Cost  of  white  labor  per  1,000 
oz.  of  precipitate 0 . 86 


Total  ....  $2 . 53 


Thus,  in  both  these  tests,  on  entirely  different  classes  of  mate- 
rial, we  get  a  uniform  result,  which  shows  strongly  in  favor  of  the 
crude-oil  method  of  melting,  at  least  as  far  as  the  Republic  of 
Salvador  is  concerned.  There  are  other  advantages  connected 
with  the  use  of  oil  which  do  not  appear  above,  but  which  should 
not  be  overlooked.  Firstly,  the  elimination  of  a  by-product  in 
the  shape  of  co*ke  ashes  from  the  wind  furnace;  and  secondly,  a 
great  saving  in  labor  and  personal  discomfort  to  the  man  who 
does  the  melting,  which  is  a  point  of  some  importance  in  a  tropical 
climate. 

E.  M.  HAMILTON. 

San  Sebastian,  Salvador,  October  22. 


TUBE-MILL  LINING 

(November  17.  1906) 

The  Editor: 

Sir — After  reading  about  the  proposed  tube-mill  lining  to 
be  used  at  the  Waihi  mine,  in  New  Zealand,  I  thought  it  would 
be  of  interest  to  your  readers  to  know  of  my  experience  with 
practically  the  same  lining.  We  have  installed  a  12-ft.  mill, 
made  in  the  shops  of  this  company  (Oriental  Con.  Mining  Co., 
of  Korea),  and,  being  slightly  out  of  the  world,  it  would  have  been 


Fig.  21.      1,     2,     3,     4.     Rails.     5.  Quartz.     6.  Mortar.     7.   Shell. 


Fig.  22.     Tube-Mill  Lining. 


a  great  saving  to  line  our  mill  with  ordinary  hard  quartz  and  cement 
such  as  described  in  the  MINING  AND  SCIENTIFIC  PRESS  of  July 
28,  1906. 

About  nine  months  ago  it  occurred  to  me  that  if  we  could 
utilize  our  hard  quartz,  together  with  a  proper  cementing  material, 
it  would  make  an  ideal  lining  for  a  tube-mill.  The  most  im- 
portant point  was  how  to  hold  it  in  place  within  the  tube.  The 


TUBE-MILL  LINING.  167 

mill  was  put  together  in  three  sections  or  sheets  of  iron  and  all 
well  riveted  hot.  These  sections  we  well  knew  would  not  be  as 
good  as  one  continuous  sheet  or  tube,  for  they  were  liable  to  spring 
a  leak  around  the  rivets.  This  would  mean  a  considerable  loss 
in  our  case,  as  we  are  grinding  concentrate  to  a  slime  in  strong 
cyanide  solution.  Therefore  an  arrangement  that  would  give 
strength  to  the  mill  as  well  as  hold  in  place  the  'bull'  quartz  lining 
was  wanted.  Sixteen-pound  rails  were  riveted  lengthwise  in  the 
tube,  six  inches  apart  and  around  the  total  inner  circumference. 
Diameter  of  tube  is  three  feet.  Fig.  21  and  22  show  the  arrange- 
ment of  rails  and  the  way  the  quartz  and  cement  was  held  in  place. 

The  best  quartz  for  the  purpose  was  found  at  the  Tabowie  mine. 
It  was  hard  but  not  brittle,  which  seemed  to  be  an  important 
point  in  such  a  lining.  All  cementing  material  was  made  up  of 
equal  parts  of  hard  coarse  quartz,  sand,  and  cement.  Special 
care  was  taken  to  have  the  sand  clean  and  fresh.  A  layer  of  cement- 
ing material  was  first  put  between  the  rails  next  to  the  shell,  and 
spread  out  evenly.  Next,  large  pieces  of  'bull'  quartz,  2  and  3 
in.  diam.  were  pressed  into  the  cement  as  compactly  as  possible, 
and  between  these  larger  pieces  smaller  quartz  was  filled  in  with 
the  cementing  material.  It  was  all  tamped  well,  so  as  to  fill  the 
spaces  with  cement.  Another  layer  of  cement  was  spread  evenly 
over  the  top  and  another  layer  filled  in  as  before.  The  two  layers 
brought  the  quartz  about  two  inches  above  the  rails,  the  upper  layer 
serving  as  a  protection.  Every  little  space  between  the  large  quartz 
was  filled  with  quartz  and  cementing  material.  Finally,  on  top 
of  all  was  placed  the  mortar;  this  also  was  well  tamped.  The 
surface  was  smoothed  with  a  trowel  and  then  allowed  to  set. 
A '  strip  or  one-third  of  the  mill  was  lined  at  one  time.  After 
two  days  it  became  sufficiently  hard  so  that  the  mill  could  be 
turned  over  and  another  one-third  lined  in  the  same  way.  When 
the  lining  was  complete,  it  was  allowed  to  set  for  six  weeks.  This 
was  more  than  was  really  necessary  to  become  hard,  but  we  wanted 
to  have  it  thoroughly  dried  out,  so  as  to  have  it  in  the  best  possible 
condition  to  wear.  The  inner  diameter  of  tube  was  now  about 
2  ft.  3  in.  Ordinary  bull  quartz,  the  same  as  used  for  the  lining, 
was  broken  up  in  2  and  3-in.  pieces  and  used  as  pebbles  for  grinding, 
which  proved  to  be  very  satisfactory.  The  tube  was  filled  just  a 
little  over  half  full,  which  amounted  to  1£  to  2  tons  of  pebbles. 
The  material  ground  in  the  mill  was  concentrate,  cyanide  solution 
being  used. 


168  RECENT  CYANIDE  PRACTICE. 

Now,  in  regard  to  the  wearing  of  the  lining,  I  can  say  that 
it  was  by  no  means  satisfactory.  At  the  rate  it  was  wearing 
it  would  have  only  taken  about  two  weeks  to  cut  away  all  the 
lining.  It  was  rapidly  undermining  the  larger  pieces  of  quartz — 
that  is,  the  cementing  material  was  gradually  cut  out.  Wherever 
there  was  a  space  of  cement  between  the  quartz  that  was  possible 
to  wear,  it  was  sure  to  be  gradually  worn  away  and  cut  out,  allowing 
the  quartz  pieces  to  fall  out.  You  cannot  imagine  the  beating 
and  wearing  action  the  pebbles  have  on  that  cementing  material. 
The  quartz  in  the  lining  will  stand  alright,  but  the  thing  is  to  keep 
it  in  place.  Even  with  silex  linings,  where  the  best  quality  of 
diamond  cement  is  used,  and  where  all  the  bricks  are  made  to  fit 
as  closely  as  possible,  the  pebble  will,  in  spite  of  all,  wear  away 
some  of  the  cement  to  a  certain  depth.  Now,  how  can  you  ex- 
pect ordinary  or  portland  cement  to  stand  where  the  spaces  between 
rough  pieces  of  quartz  are  greater?  It  may  be  easy  to  think 
in  the  first  place  that  this  lining  is  going  to  hold,  but  to  make  it 
is  another  thing.  The  lining  appeared  to  be  very  hard  before 
using  and  certainly  ought  to  have  been,  for  it  had  plenty  of  time 
to  set.  The  principle  of  the  lining  is  all  right,  but  I  am  afraid 
we  will  have  to  find  something  a  good  deal  harder  than  portland 
cement  for  a  cementing  material. 

Cast-steel  liners  were  the  next  to  be  tried,  as  we  had  on  hand 
enough  of  stamp-battery  liners  (4  ft.  by  9  in.  and  1  in.  thick) 
for  our  purpose.  Before  putting  them  in  place  the  old  quartz 
lining  had  to  be  removed  from  between  the  rails  by  means  of  a 
single  jack  and  moil.  It  was  no  easy  task,  for  it  was  hard  and  the 
rails  held  it  in  securely.  The  rails  were  left  in  and  the  steel  plates 
put  on  top,  being  held  in  place  by  bolts  with  counter-sunk  heads. 
The  bolt  extended  out  through  the  shell,  and  over  this  was  put 
a  washer  made  from  a  piece  of  old  vanner  belt.  On  top  of  this  was 
an  iron  washer  and  then  the  nut.  There  were  two  bolts,  one  in 
each  end  of  the  plate,  to  hold  it  in  place,  and  both  were  screwed 
down  tightly.  After  a  day  or  so  of  running,  they  were  screwed 
up  again.  Probably  it  was  necessary  to  go  all  over  the  bolts  on 
the  tube-mill  a  third  time,  but  after  this  we  never  had  any  trouble 
with  bolts  leaking  or  getting  loose.  It  was  absolutely  necessary 
to  have  vanner-belt  washers  next  to  the  shell.  Fig.  23  will  show 
the  method  of  holding  the  liners. 

The  rails  give  the  tube  great  strength,  especially  where  it  is. 


TUBE-MILL  LINING.  169 

put  together  in  three  sections.  With  these  in  place,  there  need 
be  no  fear  of  leaks  starting  around  rivets,  especially  if  the  riveting 
has  been  done  well. 

These  steel  liners  have  now  been  in  use  one  month  and  show 
only  a  little  wear.  At  the  present  rate  of  wear  these  liners  should 
last  at  least  six  or  seven  months  more.  About  ten  tons  of  clean 
concentrate  per  day  pass  through  our  12-ft.  mill.  Two  tons  out 
of  the  ten  are  caught  by  the  spitzkasten  box  and  passed  through 


Fig.  23.      1.  Steel     Plate     Liner.     2.  Countersunk     Head.     3.  Steel     Rail. 
4.   Vanner-belt  Washer.          5.  Iron  Washer.          6.   Nut. 


the  mill  again  as  coarse  concentrate,  making  eight  tons  ground 
to  slime  and  passing  into  the  agitators  per  24  hours.  The  ques- 
tion of  a  cheap  lining  in  out-of-the-way  places  like  Korea  is  cer- 
tainly one  of  great  importance  to  tube-milling.  If  more  would 
give  their  experiences  concerning  different  linings,  it  would  be  of 
great  value  to  us  all. 

A.  E.  DRUCKER. 
Taracol,  Korea,  September  29. 


A  SIMPLE  SOLUTION  METER 
BY  E.  H.  NUTTER 

(December  1,  1906) 

In  the  operation  of  cyanide  plants,  it  is  nearly  always  import- 
ant to  have  a  means  of  correctly  determining  the  amount  of  gold- 
bearing  solution  entering  the  precipitating  boxes.  In  some  plants 


SOLUTION  MLTE.R 


Fig.   24. 

this  is  done  by  alternately  filling  and  discharging  sump-vats  of 
fairly  good  size,  and  recording  the  height  of  solution  each  time  a 
sump  is  filled.  This  is  a  clumsy,  though  accurate  enough,  method, 
but  has  the  objection  that  it  requires  nearly  constant  attendance. 


A  SIMPLE  SOLUTION  METER.  171 

Various  water  meters  are  manufactured  which  can  be  used  for 
solution  work,  except  that  those  of  sufficient  capacity  are  expen- 
sive, and  are  open  to  the  objection  that  the  lime  which  is  used 
in  practically  all  cyanide-plant  solutions,  soon  deposits  a  scale 
in  the  working  parts  of  the  meters,  which  renders  them  inaccurate 
or  puts  them  out  of  business  altogether. 

To  meet  these  objections  I  adapted  the  familiar  sampling 
box  illustrated  herewith,  to  the  requirements  of  the  case,  and 
one  was  installed  as  a  meter  at  the  Liberty  Bell  mill.  The  device 
is  simple  and  cheap,  and  as  others  may  find  it  useful,  a  description 
of  it  is  not  out  of  place. 

The  arrangement  can  be  seen  by  reference  to  Fig.  24.  The 
compartments  B  Bf  alternately  take  the  solution  flow  from  the 
feed-pipe.  As  a  compartment  fills,  the  weight  of  solution 
overbalances  the  empty  compartment  and  the  box  turns  through 
a  short  arc,  discharging  as  it  turns,  until  it  is  stopped  by  the 
springs  S'S'.  Each  time  B'  discharges  the  counter  registers  1. 
The  meter  at  the  Liberty  Bell  is  set  up  over  a  vat,  and  the  pans 
shown  in  the  diagram  are  always  submerged.  Their  retarding 
effect  is  necessary  to  avoid  excessive  jar.  A  dash-pot  would  prob- 
ably do  as  well,  or  else  the  box  could  be  made  of  metal  with  a 
pear-shaped  cross-section,  and  hung  close  up  to  its  centre  of 
gravity.  The  latter  form  would  not  need  the  springs  or  pans. 

At  the  Liberty  Bell,  the  constant  of  the  meter  was  determined 
by  filling  the  vat  under  it  and  dividing  by  the  number  of  double 
discharges  registered.  In  this  way  leakage,  splash,  and  all  other 
irregular  factors  are  averaged,  and  determined.  The  constant  so 
determined  was  0.32275  tons  for  each  unit  registered.  This 
meter  handles  the  flow  from  an  80-stamp  mill  crushing  in  cyanide 
solution.  For  this  size  of  meter  the  pans  should  be  at  least  36  in. 
diam.,  and  the  springs  made  of  not  less  than  J-in.  rod.  A  four-inch 
hole  in  the  bottom  of  each  pan  tends  to  steady  its  motion  through 
the  solution. 


PROGRESS  IN  CYANIDATION 

(Editorial,  December  15,  1906) 

The  article  on  'Recent  Improvements  in  the  Cyanide  Process* 
by  Mr.  F.  L.  Bosqui,  will  command  attention,  being  written  by 
one  who  is  in  the  thick  of  current  practice.  Mr.  Bosqui  favors  filter- 
ing machines  of  the  Moore-Butters  type  and  is  inclined  to  con- 
sider, as  Mr.  Alfred  James  does,  that  filter-presses  will  shortly  be 
relegated  to  the  background.  This  appears  open  to  doubt.  Two 
large  facts  are  against  it,  namely,  the  continued  use  of  presses  at 
Kalgoorlie  and  the  successful  improvements  recently  made  by 
Mr.  C.  W.  Merrill  at  the  Homestake.  From  Kalgoorlie  we  hear 
good  news  of  the  Ridgway  invention,  a  horizontal  revolving 
automatic  vacuum  filter,  but  this  machine  has  yet  to  be  tried  in 
the  United  States.  At  present,  of  all  the  sand  leached  at  Kal- 
goorlie only  a  few  thousand  tons  are  treated  by  devices  other  than 
filter-presses.  All  the  larger  mines  in  the  back  country  use  triem 
and  the  Ivanhoe  is  now  erecting  a  new  filter-press  plant.  Filter- 
pressing  at  Kalgoorlie  now  costs  about  35  cents  per  ton,  and 
leaves  12  to  15  per  cent  moisture  in  the  cakes;  it  is  believed  locally 
that  a  new  plant  on  a  large  scale  could  be  operated  for  not  more 
than  25  cents  per  ton.  Of  course,  in  regions  where  water  costs 
nothing  and  the  original  slime  is  docile  to  treatment,  the  filtering 
machines  will  make  a  better  comparison  with  presses.  Meanwhile, 
Mr.  Merrill's  work  is  bound  to  encourage  the  advocates  of  the  older 
method.  He  has  enlarged  its  scope  and  simplified  its  details. 
With  24  filter-presses,  each  weighing  65  tons,  aiid  each  of  26-ton 
capacity  (as  compared  to  the  old  6-ton  presses),  he  expects  the 
total  cost  of  treating  slime  to  be  not  more  than  25  cents  per  ton. 
The  mills  make  1,600  tons  daily  of  this  product,  and  2,400  tons  of 
sand.  A  test  has  been  made  on  6,000  tons  of  slime.  In  charging, 
he  uses  a  pressure  of  35  pounds;  while  leaching,  12  to  15  pounds;  and 
to  sluice  with,  a  pressure  of  65  pounds  per  square  inch.  Out  of  a  slime 
containing  91  cents,  he  extracts  83  cents.  Mr.  Bosqui  gives  other 
details ;  those  we  quote  are  from  Mr.  Merrill  himself.  It  is  a  remark- 
able fact,  worthy  of  note,  that  after  28  years  working,  35  per  cent 
of  the  Homestake  ore  still  comes  from  surface  excavations.  An- 
other matter  under  trial  is  the  use  of  zinc  dust  as  against  shaving ; 


PROGRESS  IN  CYANIDATION.  173 

the  former  is  gaming  ground  in  America.  We  are  informed  that 
at  the  Waihi,  treating  25,000  tons  per  month,  it  requires  seven 
men  continuously  to  clean  the  boxes,  using  zinc  shaving;  at  the 
Homestake,  treating  45,000  tons  per  month,  only  four  men  are 
employed  a  half-day,  using  zinc  dust.  In  all  these  matters  there  is 
a  constant  effort  to  improve,  and  it  is  only  by  unprejudiced  tests 
that  the  best  method  can  be  determined.  On  another  page, 
Mr.  E.  H.  Nutter  adds  greatly  to  the  value  of  our  Discussion 
Department  by  a  letter  in  which  he  compares  the  use  of  the  Moore 
and  Butters  niters.  Such  first-hand  information  from  practical 
men  will  be  of  service  to  all  those  who  use  cyanide  in  milling.  We 
trust  other  friends  will  not  hesitate  to  put  their  experiences  on 
record,  where  it  can  be  of  general  service. 


CYANIDE  PRACTICE  WITH  THE  MOORE  FILTER 

(December  15,  1906) 

The  Editor: 

Sir — Mr.  R.  Oilman  Brown's  recent  contribution  to  the  liter- 
ature of  vacuum  filtering,  entitled  'Cyanide  Practice  with  the 
Moore  Filter,'  appearing  in  your  issues  of  September  1  and  8,  is 
one  of  the  few  articles  that  have  been  published  on  the  subject 
of  increasing  interest  and  growing  importance  to  those  who  have 
to  face  difficult  problems  in  cyanidation.  Of  the  few  articles  so 
far  published,  Mr.  Brown's  is  by  far  the  most  thoughtful,  and  con- 
tains detail  that  others  have  not  attempted  to  give. 

As  the  writer  had  more  or  less  to  do  with  the  construction  of 
the  Bodie  plant,  and  its  subsequent  operation,  and  since 
then  has  had  the  opportunity  of  comparing  it  with  the  Butters- 
Cassel  installation  at  the  Combination  mine,  Goldfield,  Nevada, 
the  Butters'  plant  at  Virginia  City,  and  the  Moore  plant  at  the 
Liberty  Bell  mill  at  Telluride,  Colorado,  he  has  gathered  a  few 
facts  pertinent  to  the  discussion  that  may  be  of  some  interest. 

At  the  Standard,  silex  blocks  for  tube-mill  lining  were  a 
failure ;  at  the  Liberty  Bell  they  are  a  success.  The  difference 
in  results  can  apparently  be  attributed  entirely  to  the  different 
pebbles  used — to  the  difference  in  the  thickness  of  the  material 
fed  to  the  tube-mills — and  to  laying  the  silex  blocks  edgewise 
instead  of  flatwise,  in  the  later  lining.  The  other  factors  affecting 
the  life  of  the  lining  can  be  neglected,  in  this  comparison,  as  the 
silex  blocks  are  of  the  same  grade,  and  look  to  be  from  the  same 
quarry ;  the  speed  of  the  mills  is  the  same ,  and  it  would  be  hard  to 
find  two  ores  more  nearly  the  same  (with  regard  to  the  percentage 
of  hard  quartz  and  soft  slime-forming  material)  than  the  Liberty 
Bell  and  the  Standard  Consolidated  ores. 

At  the  time  the  silex  was  tried  at  the  Standard,  local  pebbles 
of  miscellaneous  character,  and  largely  of  igneous  origin  were  in 
use.  Their  consumption  was  about  50  Ib.  per  ton  of  sand  re- 
ground.  To  a  large  extent  they  wore  flat,  indicating  a  sliding 
rather  than  a  rolling  motion.  At  that  time  the  tube-mill  was  fed 
almost  entirely  from  spitzkasten  underflow,  carrying  perhaps 
20  to  25%  solids.  The  silex  was  2\  in.  thick,  and  the  lining  lasted 


CYANIDE  PRACTICE  WITH  THE  MOORE  FILTER.     175 

six  weeks.  At  the  Liberty  Bell,  a  2J-in.  silex  lining  in  a  mill  fed 
from  spitzkasten  underflow  gave  four  months  of  actual  service. 
As  all  other  conditions  were  practically  parallel  in  the  operation 
of  these  two  mills,  except  the  use  of  local  pebbles  in  one  and  flint 
pebbles  in  the  other, the  short  life  of  the  silex  at  the  Standard  can, 
it  seems,  be  blamed  entirely  on  the  local  pebbles  used. 

At  the  Liberty  Bell  there  are  three  tube -mills,  one  fed  by 
spitzkasten  underflow  as  already  stated,  while  the  others  receive 
the  discharge  from  Dorr  scraping  classifiers,  a  coarse  product  carry- 
ing from  45  to  50%  solids.  In  these  mills,  also,  the  silex  blocks 
have  been  set  on  edge,  forming  a  lining  four  inches  thick.  By 
setting  the  blocks  edgewise,  it  seems  likely  that  the  wear  is  increased 
as  the  bedding  planes  of  the  original  limestone  seem  to  be  parellel 
to  the  flat  sides  of  the  blocks.  Capping  is  certainly  not  so  bad 
with  the  edgewise  blocks.  The  edgewise  lining  has  already  had 
nine  months  of  actual  service,  and  seems  good  for  several  months 
more.  Roughly,  the  lining  in  the  mill  receiving  spitzkasten  under- 
flow wore  at  the  rate  of  one  inch  in  two  months,  as  there  was 
some  waste,  of  course,  when  it  was  finally  removed.  In  the  other 
mills  the  rate  of  wear  has  been  just  about  half  of  this  or  one  inch 
in  four  months.  Here,  then,  are  three  mills  on  the  same  ore, 
and  operating  under  nearly  identical  conditions,  except  for  the 
matter  of  thickness  of  pulp  fed.  In  the  mills  receiving  the  thicker 
pulp  the  wear  of  linings  is  about  half  that  in  the  other.  The  duty 
of  the  four-inch  lining  has  been  something  over  9,000  tons  of  sand 
re -ground  per  inch  of  wear. 

These  facts  are  again  illustrated  by  later  results  with  the 
tube-mill  at  the  Standard.  There,  the  first  wrought -iron  lining 
of  J-in.  plates  lasted  90  days  and  re-ground  about  4,800  tons  of 
sand.  During  its  life  only  a  small  tonnage  of  pond-tailing  was 
introduced  to  the  mill.  About  the  time  the  second  lining  of  the 
same  kind  was  put  in,  arrangements  had  been  completed  for  in- 
troducing pond-tailing  in  addition  to  the  daily  mill  tonnage,  up 
to  the  full  capacity  of  the  filtering  plant.  The  percentage  of 
solids  in  the  tube-mill  feed  during  the  life  of  the  second  lining 
averaged  around  45%,  as  against  20  to  25%  before.  The  life  of 
the  second  lining  was  170  days  as  against  90;  the  total  tonnage  of 
re-ground  sand  increased  from  4,800  to  over  10,000,  and  the  pebble 
consumption  dropped  from  6.5  Ib.  per  ton  to  2.6  Ib.  All  other 
conditions  were  the  same.  These  results  speak  for  themselves. 


176  RECENT  CYANIDE  PRACTICE. 

At  the  Standard,  the  cost  for  local  pebbles  at  $9  per  ton  laid  down 
at  the  tube-mill  was  $0.225  per  ton  of  re-ground  sand,  while  the 
cost  for  flint  pebbles  under  the  same  conditions  at  $70.20  per  ton 
of  2,000  Ib.  laid  down  at  the  tube -mill  was  only  $0.233  per  ton 
re-ground,  and  this  has  since  dropped  to  $0.091  per  ton.  Good 
technical  results  have  been  obtained  with  the  Moore  plant  at  the 
Standard  during  the  last  half-year.  The  extraction  has  been 
increased  and  the  cost  lowered.  These  results  are  entirely  to  the 
credit  of  Mr.  H.  H.  Kessler,  who  had  been  in  charge  of  the  plant 
since  the  first  of  the  year. 

At  the  Standard,  during  the  time  the  tube-mill  was  shut  down 
waiting  for  the  cement  to  harden  in  the  silex  lining,  the  Moore 
plant  limped  along  as  best  it  could  without  re -grinding.  The 
sand  accumulated  wherever  it  had  a  chance.  The  settlers,  the 
agitators,  and  the  filtering  vats  all  furnished  their  quota  of  sand 
and  grief.  A  crew  of  about  six  men  was  kept  busy  all  the  time 
repairing  filters,  and  this  one  month  alone  made  a  decided  increase 
in  the  costs  for  the  whole  year. 

Mercury-step  bearings  for  the  agitator  shafts  were  a  good  deal 
of  a  failure.  The  balls  ground  the  iron  and  the  mercury  together 
into  a  nice  iron  amalgam,  and  their  use  was  abandoned. 

Mr.  Brown  has  described  the  basket  hoisting  arrangement  at 
the  Standard.  At  the  Liberty  Bell,  the  baskets  are  hoisted  for 
transfer  by  means  of  hydraulic  cranes,  operated  under  a  pressure 
of  250  Ib.  These  work  well,  and  give  much  less  trouble  than  the 
differential  chain  hoists  at  the  Standard.  Where  high-pressure 
water  is  not  available,  an  automatic  high-pressure  pump  installa- 
tion, such  as  is  used  for  elevator  service,  could  be  utilized.  At 
the  Liberty  Bell  also,  an  independent  electric  motor  drive  is  used 
for  traversing  the  cranes.  This  is  much  the  best  arrangement 
where  one  crane  serves  a  number  of  baskets.  The  long  filter  as 
installed  at  the  Standard  did  fairly  good  work,  but  there  was,  never- 
theless, considerable  trouble  from  twinning  or  coalescing  of  the 
cakes  on  adjoining  filters,  which  prevented  efficient  washing. 
The  filters  continually  broke  loose  from  the  spacing  bars,  and  before 
the  writer  left  Bodie  he  was  seriously  considering  the  advisability 
of  dividing  each  of  the  16-ft.  filters  into  two  units  and  stretching 
the  canvas  on  iron  frames.  This  was  not  done,  but,  from  the  ex- 
perience elsewhere  with  the  smaller  filters,  it  would  be  an  improve- 
ment. Mr.  Brown  has  called  attention  to  the  greater  efficiency 


CYANIDE  PRACTICE  WITH  THE  MOORE  FILTER.  177 

of  the  filtration  when  the  pulp  is  thick.  This  is  a  matter  that  should 
not  be  overlooked  in  the  design  of  filtration  plants,  as  it  affeccs 
the  capacity  in  a  very  large  degree.  The  reason  seems  to  be  mainly 
that  in  the  thicker  pulps  the  sand  is  buoyed  up,  and  a  better  and 
more  permeable  admixture  of  sand  and  slime  is  obtained  in  the 
cakes. 

It  is  satisfactory  to  record  that  the  estimated  capacity  of 
the  Standard  plant  of  3,000  tons  per  month  has  been  exceeded 
by  500  tons  during  the  months  when  uninterrupted  excavation 
could  be  carried  on  in  the  ponds.  Mr.  Brown's  statement  that 
there  was  no  accumulation  of  weak  solution  in  the  plant,  applied 
to  the  first  period  of  the  operations.  After  all  sources  of  mechan- 
ical loss  of  solution  had  been  eliminated  there  was  a  constant  accu- 
mulation of  weak  solution,  which  had  to  be  run  to  waste.  Mr. 
Brown  makes  incidental  mention  of  the  Butters-Cassel  process 
as  being  an  inversion  of  the  Moore  process,  and  points  out  the 
common  essential  feature  of  the  two,  which  is,  the  adhesion  to 
the  filter  of  a  cake  of  slime,  thereby  making  possible  its  removal 
from  the  unfiltered  remaining  pulp.  In  the  Moore  process  the 
filters  are  transferred  from  loading  to  washing  vat,  etc.,  and  back 
again,  while  in  the  Butters-Cassel  process  the  filters  are  stationary, 
and  the  pulp,  wash- water,  etc.,  are  transferred  to  and  from  the 
filtering  vat.  When  large  capacity  can  be  obtained  from  a  rela- 
tively small  filtering  plant,  the  Butters-Cassel  process  has  several 
advantages  over  the  Moore  process,  but  where  the  filtering  plant 
must  be  large  the  reverse  is  true. 

It  must  be  borne  in  mind  that  there  is  a  wide  variation  in 
the  slimes  made  from  different  ores  and  that  they  act  differently 
in  filter-plants,  so  that  a  plant  designed  to  handle  a  certain  ton- 
nage at  one  mine  will  have  a  different  capacity  at  another.  Thus 
at  the  Combination  mill  at  Goldfield,  the  loading  period  is  only 
30  minutes,  while  at  the  Standard  it  varies  from  2£  to  6  hours, 
depending  on  the  proportions  of  clay  slime  and  fine  sand  in  the 
charge,  and  the  thickness  of  pulp.  Therefore,  a  plant  designed 
to  handle  60  tons  per  day  of  Combination  slime  would  fall  far  short 
of  handling  60  tons  of  Bodie  slime.  At  the  Liberty  Bell  the  load- 
ing period  is  one  hour,  while  at  Butters'  Virginia  City  plant,  the 
time  varies  from  30  minutes  to  one  hour.  At  all  of  the  plants 
it  is  the  aim  to  build  up  a  cake  of  from  f  to  1  in.  thick. 


178  RECENT  CYANIDE  PRACTICE. 

It  will  be  assumed  here  that  the  essential  operations  of  load- 
ing, washing  the  cake,  and  discharging  in  water,  will  require  the 
same  length  of  time  with  the  two  processes  on  the  same  slime, 
and  this  discussion  is  consequently  narrowed  to  a  consideration 
of  the  relative  merits  of  transferring  the  filters  and  transferring 
the  pulp,  wash-water,  etc.  It  is  true  that  with  the  Butters  proc- 
ess a  somewhat  higher  vacuum  can  be  maintained  within  the 
filter,  on  account  of  the  possibility  of  arranging  for  bottom  solu- 
tion discharge  from  the  filters,  which  cannot  be  done  easily  with 
the  Moore  process.  The  difference  is  not  great,  however,  as  the 
solution  is  raised  in  the  suction  pipe  in  the  Moore  niters  on  the 
principle  of  the  air-lift,  and  there  is  not,  consequently,  a  solid 
column  of  solution,  reducing  the  vacuum  foot  for  foot  of  lift  in 
the  suction  pipe.  The  rate  of  loading,  also,  does  not  increase 
directly  with  the  vacuum,  but  is  greater  at  times  with  a  lower 
than  with  a  higher  vacuum. 

At  the  Liberty  Bell,  when  everything  is  working  smoothly,, 
the  Moore  plant  will  just  about  hold  even  with  the  mill  crushing 
350  tons  per  day.  In  order  to  give  the  cakes  a  preliminary  weak 
solution  wash  and  allow  also  for  repairs,  another  set  of  niters 
and  another  washing  vat  are  to  be  installed.  Besides  the  neces- 
sary settlers  and  agitators,  the  plant  at  present  contains  six  vats,. 
two  of  which  are  for  loading,  and  five  baskets  or  filter  sets.  The 
baskets  are  transferred  by  two  overhead  traveling  hydraulic 
cranes,  and  each  transfer  takes  ten  minutes.  Each  complete  cycle 
requires  two  hours  and  forty  minutes,  divided  as  follows:  One 
hour  and  ten  minutes  loading  and  transferring;  one  hour  and 
thirty  minutes  washing,  discharging,  and  transferring  back  to 
loading  vat.  The  time  required  for  a  cycle  with  the  Butters- 
Cassel  process  depends  on  the  time  required  for  transferring  pulp, 
water,  etc.,  which  is  dependent  on  the  size  of  vats  and  pumps. 

To  arrive  at  a  comparison,  let  it  be  assumed  that,  the  Lib- 
erty Bell  plant  is  to  be  changed  from  the  Moore  to  the  Butters, 
system.  Instead  of  the  present  arrangement  of  two  loading 
and  four  washing  vats,  these,  and  the  additional  ones  necessary 
will  be  used  for  all  operations.  At  Virginia  City  the  time  of  fil- 
tering and  emptying  the  filtering  vats  is  from  15  to  20  minutes. 
At  the  Combination  it  is  from  15  to  25  minutes.  Each  filtering 
vat  at  the  Liberty  Bell  contains  3,050  cu.  ft.  A  6-in.  centrif- 
ugal pump  at  normal  speed  would  fill  or  discharge  a  vat  in  approx- 


CYANIDE  PRACTICE  WITH  THE  MOORE  FILTER.  179 

imately  28  min.,  a  7-in.  pump  in  18  min.,  an  8-in.  pump  in  14  min., 
and  a  10-in.  pump  in  7.5  minutes.  The  large  pumps  involve  the 
use  of  large  valves,  which  are  a  source  of  trouble  in  pumping  sand, 
while  the  smaller  pumps  involve  a  larger  plant.  For  a  middle 
course,  let  us  consider  the  installation  of  7-in.  pumps.  It  will 
practically  be  necessary  to  install  a  pump  to  each  vat,  in  order 
to  avoid  undue  valve  complications.  The  cycle  for  each  vat, 
then,  will  be  as  follows:  Loading  one  hour,  pumping  out  pulp 
18  min.,  pumping  in  water  18  min.,  washing  the  cake  one  hour, 
discharging  15  min.,  pumping  back  water  18  min.,  pumping  in 
pulp  18  min.,  total  3  hr.  27  min.,  say  3  hr.  30  min.,  as  that  much, 
if  not  more,  extra  time  will  easily  be  consumed.  This  cycle  is 
longer  by  50  min.  than  with  the  Moore  plant.  At  45  filter- 
charges  per  day — the  usual  run — there  is  a  total  time  increase  of 
37  hr.  30  min.  required  to  handle  the  tonnage,  and  provision  will 
have  to  be  made  to  handle  11  extra  charges  per  day  over  what 
the  present  plant  would  take  care  of.  This  means  the  installation 
of  three  more  filter  sets  and  two  more  vats.  In  addition,  two 
storage  vats  would  have  to  be  provided,  one  for  water  and  one  for 
pulp  for  taking  care  of  the  flux  of  material  during  operation. 
These  should  have  a  capacity  of  at  least  6,000  cu.  ft.  each,  and 
more  than  this  would  be  desirable.  We  have,  then,  two  filtering 
vats  of  3,000  cu.  ft.  capacity,  three  additional  baskets,  eight  7-in. 
centrifugal  pumps,  with  the  necessary  pipe  connections,  three-way 
and  single  valves,  belting,  line  shafting,  motor  drive,  etc.,  and  a 
light  crane  for  handling  filters  for  repairing;  and  two  storage  vats 
of  not  less  than  6,000  cu.  ft.  capacity  each,  all  of  which  are  bal- 
anced against  two  heavy  traveling  hydraulic  cranes,  with  the  neces- 
sary heavy  track  supports.  Roughly,  the  first  cost  would  be  about 
$6,000  at  Telluride  in  favor  of  the  Moore  process.  The  chief 
expense,  however,  amounting  to  more  than  the  increased  first  cost, 
would  be  the  power  cost  for  driving  the  centrifugal  pumps.  The 
power  required  for  pumping  would  vary  from  a  minimum  at  the  be- 
ginning to  a  maximum  at  the  end  of  the  transferring  period,  com- 
plicated of  course  by  the  workings  of  the  various  pumps,  to  the 
extent  of  their  effect  on  the  height  of  material  in  the  storage  vats. 
At  the  Liberty  Bell,  any  arrangement  that  could  be  made  without 
the  reconstruction  of  the  present  filtering  vats,  would  necessitate 
each  pump  working  against  a  maximum  head  of  19  ft.,  and  each 
pump  would  then  take  about  11  h.p.  part  of  the  time.  As  power 


180  RECENT  CYANIDE  PRACTICE. 

is  bought  on  peak  load  in  the  Telluride  district  and  cost  a  mini- 
mum of  $5  per  horse-power  month,  it  would  be  hard  to  say  what 
the  extra  power  bill  would  be.  Should  four  pumps  be  working 
near  the  maximum  lift  at  one  time,  which  would  not  be  unlikely, 
the  bill  for  the  month  would  be  about  $225.  It  would  probably 
not  be  less  than  $150  any  one  month,  and  might  run  up  to  $300 
or  $400.  There  would  be  no  saving  in  labor  in  one  plant  over 
the  other,  as  one  man  on  a  shift  would  be  required  to  attend  to 
the  filtering  in  either  case. 

EDWARD  H.  NUTTER. 
Telluride,  November  25. 


RECENT  IMPROVEMENTS  IN  THE  CYANIDE 

PROCESS 
BY  F.  L.  BOSQUI 

(December  15,  1906) 

*It  was  nearly  twenty  years  ago  that  two  Glasgow  chemists, 
MacArthur  and  Forrest,  made  the  first  practical  application  of  the 
dissolving  action  of  a  dilute  cyanide  solution  on  gold.  The  proc- 
ess was  at  once  adopted  in  New  Zealand  and  South  Africa.  In 
the  latter  country  all  the  conditions  were  most  favorable  to  its 
success;  and  the  enormous  profits  yielded  by  the  pioneer  plants 
at  once  established  cyanidation  as  a  process  of  the  greatest  com- 
mercial importance. 

The  procedure  adopted  in  the  Transvaal  was  simple  in  com- 
parison with  recent  modifications  of  the  process.  The  tailing 
from  the  stamps,  after  hydraulic  concentration  of  coarse  sand 
and  sulphides,  was  gathered  in  leaching  vats;  the  slime  that  over- 
flowed was  run  into  huge  shallow  vats,  the  surplus  water  decanted, 
and  the  slime  subjected  to  a  series  of  agitations  and  decantations, 
until  the  mineral  that  it  was  found  economical  to  extract  was 
•finally  precipitated  from  the  solution. 

At  first,  zinc  shaving  was  universally  used  as  a  precipitant, 
but  this  was  superseded  by  the  electrolytic  deposition  of  the  gold 
on  sheets  of  lead.  This  was  adopted  in  all  the  representative 
plants;  but  its  popularity  soon  waned,  owing  to  the  production 
of  troublesome  by-products,  the  awkwardness  of  the  clean-up 
and  bullion  recovery,  and  the  unsatisfactory  deposition  as  com- 
pared with  that  obtained  on  zinc.  Its  chief  advantage  was  that 
it  recovered  the  values  from  extremely  dilute  solutions,  but  this 
advantage  was  nullified  by  Betty's  discovery  that  zinc  shaving 
if  dipped  in  a  weak  solution  of  lead  acetate,  would  accomplish 
the  same  thing. 

During  recent  years,  no  radical  changes  were  made  in  the 
process  in  South  Africa.  This  was  due  to  the  serious  blow  given 
the  mining  industry  by  the  Boer  war;  and  also,  in  part,  to  the  con- 
servatism of  metallurgists  on  the  Rand  and  their  reluctance  to 


*  Revised  by  the  author  from  a  paper  read  before  the  American  Mining  Congress. 


182  RECENT  CYANIDE  PRACTICE. 

adopt  important  innovations  originating  elsewhere.  The  brothers 
Denny  were  the  first  of  the  Rand  metallurgists  to  recognize  the 
importance  of  finer  grinding,  and  their  energetic  advocacy  of 
tube-milling  and  filter-pressing  finally  resulted  in  the  acceptance 
of  Australian  methods. 

It  was  during  the  lethargy  of  cyanidation  on  the  Rand  that 
the  filter-press  and  the  tube-mill  were  introduced  in  Western 
Australia.  In  this  connection  the  interesting  fact  may  be  noted 
that  all  the  important  devices  introduced  into  cyanide  practice 
had  been  previously  used  in  other  industries.  Even  the  pipe 
distributer  used  for  distributing  tailing  in  a  leaching  vat  was  an 
adaptation  of  the  common  lawn-sprinkler.  The  filter-press  had 
been  employed  to  strain  solutions  in  the  refining  of  sugar;  the 
tube -mill  had  been  in  use  as  a  dry-grinding  machine  in  the  cement 
industry. 

The  metallurgists  of  Australia  never  took  kindly  to  decan- 
tation  in  slime  treatment,  and  the  introduction  of  the  filter-press 
was  the  result.  In  justice  to  African  operators,  however,  it  must 
be  said  that  decantation  was  well  suited  to  existing  conditions. 
The  product  they  were  handling  was  too  low-grade  to  stand  the 
prohibitive  cost  of  filter-pressing.  In  Western  Australia,  the 
filter-press  was  applied  to  a  much  richer  product,  and  one  much 
better  adapted  to  the  method. 

The  obvious  objection  to  the  old  type  of  filter-presses  is  the 
high  cost  of  installation  and  operation,  but  they  nevertheless 
enjoyed  a  great  success;  and  it  is  worthy  of  note,  in  observing 
the  evolution  of  the  process,  that  they  were  a  means  of  emphasiz- 
ing the  importance  of  fine  grinding  and  helped  to  establish  the 
tube-mill.  It  has  always  been  a  truism  in  cyanidation  that  the 
finer  the  product,  the  higher  the  extraction.  This  is  the  case 
with  but  few  exceptions.  To  apply  this  principle  required  two 
things;  an  economical  machine  for  fine  grinding  and  a  filtering 
system  that  would  be  at  once  efficient  and  economical.  You  are 
all  no  doubt  familiar  with  the  tube-mill  as  now  applied  in  cyanide 
work.  It  consists  of  a  sheet-steel  cylinder  with  cast-iron  ends, 
varying  in  size  (the  largest  mills  are  5  ft.  diam.  by  22  ft.  long), 
and  supported  either  upon  trunnions  or  upon  steel  tires  revolv- 
ing on  rollers  like  a  chlorination  barrel.  The  interior  of  the  mill 
may  be  lined  either  with  cast  iron,  or  a  species  of  natural  flint 
known  as  'silex.'  The  latter  is  the  more  commonly  used,  and 


IMPROVEMENTS  IN  THE  CYANIDE  PROCESS.      183 

is  sold  in  two  sizes;  blocks  2J  in.  and  4  in.  thick.  The  silex  lining 
is  laid  in  cement  and  will  last  from  four  to  eight  months,  depend- 
ing upon  the  ore.  When  ready  to  operate,  the  mill  is  charged 
about  half- full  with  flint  pebbles.  The  product  to  be  reduced 
is  fed  into  the  mill  either  through  a  spiral,  or  a  device  of  the  stuff- 
ing-box type,  and  the  re-ground  material  is  discharged  at  the 
opposite  end,  being  finely  comminuted  by  attrition  against  the  flint 
pebbles  and  the  lining  during  the  slow  revolution  of  the  cylinder. 
The  average  speed  of  the  tube-mill  is  from  25  to  35  revolutions 
per  minute.  The  fineness  to  which  the  sand  is  reduced  will 
depend  upon  several  factors,  chief  among  which  is  the  amount  of 
water  used.  The  best  proportion  has  been  found  to  be  one  part 
solid  to  one  part  water.  As  a  machine  for  economically  reduc- 
ing ore  to  an  extreme  fineness,  the  tube-mill  has  no  equal.  The 
cost  of  operation  is  variable.  In  this  country  and  in  Mexico  it 
will  range  between  20  and  40c.  per  ton.  •  The  work  at  El  Oro, 
Mexico,  and  at  Telluride,  Colorado,  is  representative  of  the  best 
practice  on  this  continent;  while  that  at  the  Combination  mine, 
Goldfield,  Nevada,  probably  represents  the  maximum  of  cost, 
owing  to  high  price  of  power  and  labor.  A  small  4  by  12  ft. 
trunnion  mill  is  installed  at  the  Combination  for  sliming  the  40- 
mesh  product  from  a  Bryan  mill.  The  product  of  ten  stamps, 
about  35  tons  of  ore  per  day,  passes  to  the  tube-mill  classifier; 
and  of  this  product  about  75%  goes  to  the  tube-mill,  or  24.6 
tons  per  day.  The  following  figures  may  be  of  interest: 

Cost  of  2i-in.  silex  lining  laid  in   mill $323.50 

Life    of    lining     4    months 

Cost  of  lining  per  ton  of  ore  stamped 7.7  cents 

Cost  of  pebbles  delivered  at  Goldfield $71  per  ton 

Consumption  of  pebbles 2.03  Ib.  per  ton  of  ore  stamped 

Cost  of  pebbles  per  ton  of  ore  stamped 7.1  cents 

Power  consumed 25  h.p.    at   $11.25  per  h.p.   per  month 

Cost  of  power .26.7  cents  per  ton  of  ore  stamped 

Summary,   cost  per  ton  of  ore  stamped: 

Pebbles $0.071 

Lining 0 . 077 

Power .  .  .    0 . 267 


$0.415 

Tending  the  mill  is  one  of  the  several  duties  falling  upon  one 
man,  and  the  consumption  of  lubricants  is  almost  negligible; 
therefore  I  have  not  included  these  two  items  in  the  cost.  This 
cost  of  41c.  per  ton  may  be  assumed  to  be  the  maximum  for  tube- 


184  RECENT  CYANIDE  PRACTICE. 

milling,  owing  to  the  very  high  cost  of  labor  and  transport  in 
southern  Nevada  camps. 

I  have  already  referred  to  filter-pressing  as  an  established 
practice  in  Western  Australia.  The  press  was  never  very  popu- 
lar in  America,  and  few  successful  installations  are  recorded. 
The  most  noteworthy,  perhaps,  is  that  of  the  Gold  Road  mine, 
near  Kingman,  in  Arizona,  where  two  five-ton  Dehne  presses 
have  been  successfully  operated  for  some  time.  About  three  years 
ago  Mr.  George  Moore,  after  a  series  of  failures  in  an  attempt  to 
filter-press  slime  at  the  mill  of  the  Consolidated  Mercur  Co.,  in 
Utah,  devised  a  vacuum-filter  and  installed  a  plant  in  the  Mercur 
mill.  This  was  the  origin  of  the  vacuum-filter,  recent  modifica- 
tions of  which  are  to  be  found  at  a  number  of  mills  in  this  country. 
Experiments  recently  made  in  Australia  so  far  demonstrate  the 
superiority  of  this  method  over  all  others,  that  it  seems  safe  to 
predict  the  early  disappearance  of  the  filter-press. 

The  unit  of  the  Moore  filter  is  a  rectangular  wooden  frame 
covered  with  canvas,  and  provided  with  a  vacuum  drain-pipe 
extending  to  the  lowest  point  of  the  interior.  These  frames  are 
grouped  together  in  clusters  or  baskets,  which  are  raised  and  lowered 
by  means  of  a  hydraulic  crane.  When  lowered  into  a  suitable 
compartment  containing  the  slime  pulp,  the  vacuum  is  applied 
to  a  common  pipe  connected  with  each  frame.  The  solution  is 
drawn  through  the  canvas,  and  a  slime  cake  varying  from  |  to  -J 
in.  thick  is  deposited  on  each  side  of  the  filter-leaf.  The  cluster 
of  filter-leaves  carrying  the  charge  of  slime,  weighing  several  tons, 
is  then  lifted  from  the  pulp,  shifted  automatically  to  an  adjoining 
compartment  containing  the  wash,  where  it  is  again  lowered,  the 
vacuum  applied,  and  the  displacing  operation  repeated.  The  load 
is  again  raised  and  shifted  to  a  bin  where  the  cakes  are  discharged 
by  introducing  air  into  the  interior  of  the  leaves. 

The  objections  to  the  Moore  filter  are  the  high  first  cost  of  the 
mechanism  required  to  shift  the  slime  and  the  high  cost  of  main- 
tenance. The  unmechanical  and  cumbersome  features  of  this 
system  led  to  the  introduction  by  Cassel  of  a  stationary  filter, 
and  the  elimination  of  the  awkward  mechanism  of  the  Moore 
scheme.  It  remained  for  Butters  to  adopt  the  Cassel  principle, 
simplify  it,  and  so  modify  it  as  to  make  it  a  pronounced  success  at 
his  Virginia  City  plant.  In  the  Butters  filter,  the  leaves  are  set 
in  a  rectangular  box  or  vat,  the  bottom  of  the  box  consisting  of  a 


IMPROVEMENTS  IN  THE  CYANIDE  PROCESS.     185 

series  of  pointed  pockets,  to  facilitate  the  discharge  of  the  spent 
cakes.  The  frames  are  approximately  5  by  10  ft.  and  consist 
of  a  piece  of  cocoa  matting  with  a  sheet  of  canvas  quilted  on  each 
side,  the  whole  being  stitched  on  a  frame  of  -J-in.  pipe  and  securely 
sewed  to  this  pipe-frame,  which  in  turn  is  supported  on  a  timber 
header.  The  bottom  arm  of  the  frame  is  perforated  with  small 
holes,  through  which  the  solution  enters  the  pipe  when  the  vacuum 
is  applied.  On  one  side  the  pipe  frame  is  projected  through 
the  wooden  header,  and  is  connected  with  a  common  vacuum- 
pipe  leading  to  the  vacuum-pump.  The  frames  stand  parallel 
in  the  filter-box  at  about  4J-in.  centres.  The  pulp  is  drawn  from  the 
slime-reservoir  and  pumped  into  the  bottom  of  the  filter-box  until 
all  the  frames  are  immersed.  The  vacuum  is  then  applied  until  a 
cake  of  suitable  thickness  is  deposited,  and  the  excess  of  pulp 
is  then  withdrawn  into  the  slime-reservoir.  This  operation  is 
repeated  for  the  wash,  and  the  cake  finally  discharged  into  the 
bottom  of  the  box  by  introducing  water  under  a  low  head  into  the 
interior  of  the  leaves.  The  accumulated  cakes  from  each  charge 
are  removed  by  sluicing. 

This  system  possesses  the  great  advantage  of  simplicity  and 
low  cost  of  maintenance.  A  plant  of  any  size  can  be  operated 
by.  one  man,  who  stands  on  a  platform  on  a  level  with  the  top  of 
the  filter-box  and  manipulates  the  pumps  with  levers,  and  the  valves 
with  a  simple  drum-and-sheave  mechanism.  The  200-ton  plant 
of  this  type  in  the  Butters  mill  at  Virginia  City  is  operated  at  a 
cost  of  about  lOc.  per  ton  of  slime. 

At  the  Combination  mill  40  tons  of  this  slime  per 
day  are  being  filtered  at  a  cost  of  about  45c.  per  ton,  as  follows: 

Three  men  at  $4;  $12  per  day 30  cents  per  ton 

Twelve  h.p.  at  $11.25  per  h.p.  per  month 11 

Lubricants  and  incidentals.  .  .    4       "         " 


45  cents  per  ton 

This  plant,  however,  has  a  capacity  of  56  tons  per  day.  If 
worked  to  its  limit  of  capacity,  the  cost  would  be  reduced  to  31c. 
per  ton.  The  cost  of  filter-pressing  at  the  same  plant  in  the  early 
days  of  operation  was  approximately  $1  per  ton. 

The  15  h.p.  consumed  is  used  for  the  following  purposes : 

Driving  a  4-in.  Butters  centrifugal  pump. 

Operating  a  12  by  10  Gould's  vacuum  pump. 


186  RECENT  CYANIDE  PRACTICE. 

Operating  a  2-in.  centrifugal  pump  for  raising  the  filtered 
solution  to  a  clarifying  filter-press. 

Operating  a  2-in.  centrifugal  pump  for  returning  the  slime- 
overflow  from  the  leaching- vats  to  the  slime-settlers. 

Operating  stirring  mechanism  in  two  slime-reservoirs  14  ft. 
diameter. 

The  power  may  be  distributed  as  follows : 

For  actual  operation  of  filter,  capacity  56  tons  per  day 9  h.p. 

For  agitating  slime-pump 3 

For  uses  not  connected  with  filter 3 

The  cycle  of  operation  in  the  Butters  filter  consumes  about 
3  hr.  20  min. ;  it  will  vary,  of  course,  with  the  nature  of  the  slime 
to  be  filtered. 

This  type  of  filter  has  been  installed  or  is  in  process  of  installa- 
tion at  six  mills,  in  Nevada,  Mexico,  and  Salvador. 

There  are  certain  conditions,  however,  where  the  product 
to  be  handled  is  too  low-grade  to  admit  even  of  vacuum-filtering; 
these  require  special  study  and  a  special  process.  The  need  of  a 
special  process  to  suit  a  unique  condition  was  never  better  exem- 
plified than  in  the  case  of  the  Homestake  ore. 

I  shall  not  venture  to  describe  the  different  problems  en- 
countered and  successfully  solved  by  Mr.  C.  W.  Merrill  at  the 
Homestake  in  the  cyaniding  of  a  tailing  averaging  less  than  $1.50 
per  ton.  The  next  and  most  serious  problem  to  engage  his  atten- 
tion was  the  treatment  of  the  slime,  of  which  1,600  tons  per  day 
of  an  average  value  of  80c.  per  ton  have  been  run  to  waste  from  the 
Homestake  mills.  Mr.  Merrill  has  described  a  filter-press  the 
unique  feature  of  which  is  that  it  can  be  automatically  discharged 
by  sluicing  without  being  opened,  thus  doing  away  with  the  chief 
objections  of  the  old  type  of  press,  namely,  the  cost  of  operating. 
This  press  is  of  a  common  flush-plate  and  distance  frame  pattern,, 
but  consists  of  much  larger  units.  The  dimensions  are  as  follows : 

Number  of  frames   92 

Size  of  frame 4  by  6  ft. 

Length  of  press • 45  ft. 

Capacity  of  press 26  tons 

Weight  of  press 65  tons. 

Thickness  of  cake    4  in. 

The  pulp  is  admitted  to  this  press  through  a  continuous 
channel  at  the  centre  of  the  top  of  the  frames.  When  the  cake 
is  formed,  cyanide  solution  is  forced  into  the  cake  through  channels, 


IMPROVEMENTS  IN  THE  CYANIDE  PROCESS.    187 

at  the  upper  corners.  At  the  bottom  of  the  frames,  there  extends 
a  continuous  channel  within  which  lies  a  sluicing  pipe,  provided 
with  nozzles  that  project  into  each  compartment.  This  pipe  can 
be  revolved  through  an  arc  of  any  magnitude  so  as  to  play  a  stream 
into  any  part  of  the  cake,  washing  it  down  into  the  annular  space 
between  the  central  channel  and  the  solution  pipe.  When  the 
press  is  being  filled  and  leached,  the  discharge  ends  of  this  pipe 
are  sealed.  The  method  of  operation  is  as  follows : 

The  slime,  after  partial  de-watering,  consists  of  about  three 
parts  of  water  to  one  of  solids.  In  this  form  it  is  charged  by 
gravity  to  the  presses  at  about  30-lb.  pressure.  The  leaching 
with  cyanide  solution  is  done  in  the  press,  the  effluent  solutions 
being  conducted  to  four  precipitating  vats  where  the  gold  is 
recovered  on  zinc  dust.  There  is  no  power  cost  for  agitating  or 
elevating,  except  for  elevating  the  solution  to  the  press.  There 
will  be  only  0.6  ton  of  solution  handled  per  ton  of  slime,  of  which 
only  0.3  ton  will  be  precipitated.  All  filtering  will  be  done  by 
gravity  at  a  cost  of  two  cents  per  ton. 

This  plant  is  being  erected  on  the  basis  of  tests  made  in  a  four- 
ton  press  of  the  type  described.  In  all,  1,291  tons  were  treated 
with  the  following  results: 

Average  assay- value  of  slime  before  treatment 91  cents  per  ton 

after  10     " 

Extraction  by  assay,  per  ton 81  cents  or  90% 

Recovered  in  precipitate  per  ton 83  cents  or  91% 

The  following  facts  relating  to  this  important  installation 
are  of  interest : 

Estimated  cost  of  slime-treatment   25  cents  per  ton 

Estimated  profit  per  year   $300,000 

Cost  of  plant   $400,000 

Cost  of  pipe-lines $50,000 

Area  covered  by  plant 270  by  65  ft. 

Area  covered  per  ton  of  capacity Two  square  yards 

Cost  of  installation  per  ton  of  capacity $300 

Filter-press  cost  per  ton  of  capacity $60 

Power  required 1/10  h.p.  per  ton  of  slime  treated 

Water  required  for  sluicing 4  tons  water  to  one  ton  of  slime 

In  the  elaboration  of  the  above  process  and  plant,  Mr.  Mer- 
rill shares  with  the  projectors  of  the  vacuum-filter,  the  credit 
of  the  most  noteworthy  advance  made  in  recent  years  in  the  metal- 
lurgy of  the  cyanide  process.  His  method  is  admirably  adapted 
to  Homestake  conditions;  and  its  striking  economical  features 


188  RECENT  CYANIDE  PRACTICE. 

must  appeal  at  once  to  every  engineer  and  manager  who  concerns 
himself  with  such  vital  things  as  costs  and  profits. 

Whether  an  automatically  discharged  press  can  compete 
under  average  conditions  with  the  vacuum-filter,  remains  to  be 
seen.  Much,  of  course,  will  depend  upon  local  conditions,  such  as 
the  site,  the  utilization  of  gravity  for  various  operations,  water 
facilities,  water  supply,  and  the  permeability  of  the  material 
under  treatment,  as  well  as  the  rapidity  with  which  it  yields  up 
its  precious  metal. 

Space  will  not  permit  me  to  touch  upon  zinc-dust  precipita- 
tion further  than  to  say  that  there  is  every  indication  that  it  will 
eventually  take  the  place  of  zinc  shaving  in  all  plants  of  large 
capacity.  Electric  deposition  offers  a  large  and  promising  field 
for  investigation,  but  has  not  as  yet  been  brought  to  a  perfectly 
satisfactory  conclusion.  Recent  advances  in  cyanidation  have 
mainly  to  do  with  the  finer  reduction  of  the  product  to  be  treated. 
The  treatment  of  sand  by  leaching  will  probably  continue  to  be 
the  best  method  in  a  few  instances;  but  no  observer  will  deny 
that  the  trend  of  modern  practice  is  toward  fine  grinding,  and  doing 
away  with  leaching — a  result  made  possible*  by  the  introduction  of 
the  tube-mill  and  the  efficient  filtering  methods  now  in  vogue. 


CYANIDE  PRACTICE  AT  KALGOORLIE 

(December  22,  1906) 

The  Editor: 

Sir — I  consider  it  a  fortunate  moment  when  a  copy  of  your 
issue  of  July  28  came  into  my  hands  and  enabled  me  to  read  with 
interest  and  also  a  little  amusement  an  article  by  Mr.  Alfred 
James  on  'Crushing  and  Grinding  Practice  at  Kalgoorlie.'  As 
you  mention  that  any  reply  to  Mr.  James'  criticisms  will  be  given 
a  courteous  hearing,  I  trust  that  it  will  be  so  in  this  instance. 

With  the  exception  of  a  few  remarks  in  the  first  part  of  the 
article  in  question,  there  is  little  to  disagree  with,  but  it  is  when  Mr. 
James  leaves  general  views,  and  gets  down  on  to  more  detailed 
work,  that  he  appears  to  lose  his  balance,  especially  in  regard  to  his. 
criticisms  on  the  tests  made  at  the  Ivanhoe  mine,  at  Kalgoorlie, 
between  grinding  pans  and  tube-mills.  Although  I  left  the  ser- 
vice of  that  company  in  March  last,  it  is  natural  that  an  attack  (like 
the  one  now  under  review)  on  those  experiments,  which  were  car- 
ried out  by  Mr.  R.  B.  Nicolson  and  myself,  should  evoke  a  reply. 

Taking  that  part  of  Mr.  James'  paper  which  relates  to  pans 
against  tube-mills,  he  opens  with  a  reference  to  a  mysterious  mine 
.  at  Kalgoorlie,  that  is  practising  bromo-cyanide  treatment  without 
using  bromo-cyanide  methods,  and  in  consequence  the  residues 
of  this  mine  are  reputed  to  be  worth  2J  dwt.  per  ton.  With  the 
exception  of  the  loss  in  residues,  I  have  a  shrewd  suspicion  what  the 
name  of  the  mine  is,  but  would  certainly  advise  Mr.  James  to  call 
at  headquarters  and  get  correct  figures  for  the  past  few  months, 
which  are,  I  dare  say,  considerably  under  his  estimate. 

The  question  of  extraction  was  entirely  left  out  of  the  Ivanhoe 
tests.  The  point  to  be  proved  was,  which  was  the  superior  grinder, 
a  pan  or  a  tube-mill.  Personally,  I  think  very  little  difference 
would  be  found  in  the  extraction  obtained  from  the  slime  made  by 
either  of  these  two  machines. 

I  am  glad  to  see  Mr.  James  regrets  that  names  of  such  high 
standing  should  have  been  tacked  on  to  tests  so  badly  carried  out 
as  were  those  at  the  Ivanhoe.  While  appreciating  the  compli- 
ment in  the  first  part  of  this  sentence,  I  would  also  apply  the  same 
remarks  to  Mr.  James  and  his  article.  This  same  gentleman,  by 


190  RECENT  CYANIDE  PRACTICE. 

a  wonderful  though  erroneous  deduction,  then  discovers  that  as 
the  Ivanhoe  tube-mill  worked  on  alternate  days,  the  flints  were 
coated  with  slime  at  the  start  of  each  daily  test !  For  Mr.  James, 
benefit  alone,  I  would  inform  him  that  at  the  end  of  a  day's  run 
of  the  tube-mill,  the  feed  was  shut  off  and  clean  water  passed  through 
for  some  time  before  the  mill  itself  was  stopped,  and  on  re-starting 
for  another  day's  run  the  mill  was  allowed  to  work  for  some  time 
until  its  full  load  was  reached  before  samples  of  any  kind  were 
taken.  Setting  aside  this  precaution,  the  fate  of  any  slime  left 
inside  a  tube-mill  revolving  at  32  revolutions  per  minute  can  be 
imagined. 

Mr.  James  now  comments  somewhat  sarcastically  on  the  large 
amount  of  'slime'  (?)  (-150  mesh)  which  is  allowed  to  return  to 
choke  the  tube-mill  instead  of  being  got  rid  of  at  once,  and  shows 
that  the  Ivanhoe  mill  had  more  slime  returned  than  was  its  daily 
output  of  this  product.  The  statement  made  in  the  Ivanhoe 
report  that  the  tube-mill  became  choked,  has  been  taken  perhaps 
in  too  literal  a  sense.  It  is  obvious  that  as  long  as  the  inlet  and 
outlet  of  a  tube-mill  is  large  enough,  practically  any  tonnage  of 
sand  can  be  rushed  through.  What  happens  in  a  case  of  this  kind 
is  that  the  various  spitzkasten  used  for  separating  the  resultant 
slime  and  feeding  the  mill  are  gradually  choked  by  the  accumu- 
lation of  fine  sand  returned  for  re-grinding,  the  effect  of  the 
tube -mill  having  more  original  feed  than  it  can  cope  with,  or,  in 
other  words,  the  mill  may  be  said  to  be  'overloaded.'  This  is 
what  happened  during  the  Ivanhoe  experiments.  The  tube-mill 
did  not  exactly  choke,  but  the  various  spitzkasten  employed  did, 
and  after  every  expedient  failed  the  fine  sand  was  only  prevented 
from  gradually  gaining  on  the  mill  by  reducing  the  amount  of 
original  feed.  As  there  is  a  certain  time  at  which  a  tube-mill 
must  become  overloaded,  that  particular  point  was  naturally  pre- 
sumed to  have  been  reached.  The  same  remarks  also  can  be 
applied  to  the  grinding  pans. 

At  this  point  it  may  be  as  well  to  get  an  idea  of  what  Mr. 
James  does  consider  good  work  by  a  tube-mill,  and  I  have  gone 
to  some  trouble  in  turning  up  a  few  statements  made  by  him 
during  the  last  few  years,  and  in  one  of  them  in  The  Engineering 
and  Mining  Journal  of  January,  1905,  I  notice  he  makes  the  fol- 
lowing remarks: 


CYANIDE  PRACTICE  AT  KALGOORLIE.  191 

"I  ask  why  is  it  that  the  Hannan's  Star  mill,  the  first  one 
laid  down,  should  be  still  doing  the  best  work,  while  the  Ivanhoe 
mill  has  been  thrown  out?"  And  further  on  we  have:  "The 
longest  and  oldest  mills,  those  at  Hannan's  Star,  and  the  old 
Brownhill  exhibit  the  best  results,  etc." 

Turning  now  to  the  Journal  of  the  Chamber  of  Mines  of  West- 
ern Australia  of  March,  1904,  we  see  some  working  results  of  this 
same  Hannan's  Star  mill,  which  Mr.  James  appears  to  never  tire 
in  quoting.  A  glance  at  this  latter  paper  reveals,  in  the  light  of 
present  remarks,  some  astonishing  figures,  and  I  shall  trespass  a 
little  on  your  space  to  reproduce  them  alongside  those  of  the 
Ivanhoe.  Before  giving  these  it  must  be  remembeied  that  the 
Hannan's  Star  tube-mill  was  16  ft.  long,  taking  30  h.p.,  and  was 
reducing  38  tons  of  sand  per  day  to  a  slime  of  —150,  while  the 
Ivanhoe  mill  was  13  ft.  long,  requiring  20  h.p.  and  bringing  19.5 
tons  of  sand  to  a  slime — also  of  minus  150.  It  may  be  added 
that  of  the  original  feed  of  38  tons  sent  to  the  former  mill, 
20.5%  remained  on  40  mesh,  while  of  the  19.5  tons  sent  to  the 
Ivanhoe  tube,  51%  stayed  above  40  mesh,  or,  in  other  words, 
the  original  feed  to  the  Ivanhoe  mill  was  2J  times  as  coarse  as 
that  sent  to  Hannan's  Star.  As  it  was  demonstrated,  in  tests 
carried  out  at  the  former  mine,  that  coarse  sand  had  a  bad  ef- 
fect on  tube-mill  work,  this  fact,  taking  the  size  of  the  two 
tube-mills  into  account,  explains  most  of  the  difference  in  output. 

As  'slime'  (?)  in  the  return  feed  is  the  product  that  worries 
Mr.  James  so  much,  I  give  below  the  grading  from  the  two  tube- 
mills: 

Hannan's  Star  mill  Ivanhoe  tube-mill 
(16  ft.)  268  tons  per  day,    (13  ft.)  142  tons  per  day, 
being  original  feed  and     being  original  feed  and 

sand  returned  for  re-  sand  returned  for  re- 
grinding,  grinding. 
%        Tons.                           %          Tons. 

On      40  mesh 4.5        12.06  11.40       16.19 

11        60     "        9.5       25.46  14.98       21.27 

"      100     "        19.9       53.33  36.94       52.46 

"      150     "        19.0       50.92  17.77       25.23 

Through     150  47.1     126.22  18.91       26.85 

A  glance  at  the  above  figures  shows  that  the  Hannan's  Star 
mill  with  an  original  output  of  38  tons  of  -150-mesh  slime  per 
day  contained  in  its  return  feed  no  less  than  47%,  or  126  tons 
of  this  same  objectionable  product,  against  the  Ivanhoe  mill  with 
an  original  output  of  19.5  tons,  containing  only  18.91%,  or  26.77 


192  RECENT  CYANIDE  PRACTICE. 

tons.  In  other  words,  we  have  the  extraordinary  position  of  a 
man  who  for  the  last  few  years  has  been  holding  the  Hannan's 
Star  tube-mill  up  to  the  admiration  of  the  mining  world,  exe- 
cuting a  complete  somersault,  and  condemning  the  tube-mill 
practice  on  a  neighboring  mine,  when  on  his  own  showing  this, 
latter  mill  is  doing  far  better  work,  especially  as  far  as  clean  sep- 
aration goes,  than  the  one  he  is  so  proud  of.  It  is  unfortunate 
that  Mr.  James  has  allowed  personal  feelings  to  obscure  his  judg- 
ment on  this  occasion,  and  if  he  now  puts  the  Hannan's  Star 
mill  figures  in  the  place  of  the  Ivanhoe,  it  is  evident  in  what  an 
unfortunate  position  he  has  placed  himself. 

As  it  is  hardly  necessary  to  comment  any  further  on  this, 
we  will  now  go  on  to  another  paiagraph  in  the  paper  under  re- 
view where  complaint  is  made  that  the  pans — especially  the  first 
one — had  an  undue  advantage  over  the  tube-mill  in  matter  of 
getting  rid  of  finished  product.  Surely  Mr.  James  does  not  con- 
demn 'he  practice  of  running  the  original  or  coarse  feed  into  one 
pan  and  the  return  fine  feed  into  a  second  to  be  slimed.  This 
is  one  -of  the  advantages  of  pans  over  tube-mills,  as  in  the  case 
of  the  latter  one  machine  has  to  both  reduce'  coarse  sand  and  do 
the  sliming  as  well.  However,  if  Mr.  James  had  looked  at  the 
feed  entering  the  second  or  finishing  pan  he  would  see  that  out 
of  a  daily  tonnage  of  74.6  tons  returned  to  this  pan  no  less  than 
24.5  tons  passed  150  mesh  (being  nine  tons  more  than  its  actual 
output  of  this  product),  or,  in  other  words,  this  pan  had  prac- 
tically the  same  quality  of  feed  as  the  tube-mill,  so  that  both  were 
laboring  under  the  same  disadvantage.  It  may  be  consoling  to 
the  gentleman  in  question  that  all  tube -mills  and  pans  grinding 
to  a  slime  exhibit  the  characteristic  of  having  more  -150  'slime' 
(?)  returned  to  them  than  is  their  actual  output  of  this  product 
and  it  is,  I  should  say,  the  result  of  not  having  a  proper  definition 
of  what  constitutes  slime,  and  a  better  plan  for  separation  of  the 
.same.  Numerous  attempts  have  been  made  of  late  to  define 
what  slime  is,  but  so  far  the  results  have  not  been  satisfactory. 
The  common  and  practical  definition  at  Kalgoorlie  is:  All  that 
product  which  passes  a  screen  having  150  holes  per  linear  inch. 
This,  however,  is  far  from  satisfactory,  for  anyone  conversant 
with  grinding  practice  knows  how  large  is  the  quantity  of  very 
fine  sand  that  will  pass  a  150- mesh  readily,  but  is  yet  heavy 
enough  to  sink  in  a  spitzkasten,  and  be  returned  to  the  tube- 


CYANIDE  PRACTICE  AT  KALGOORLIE.  193 

mill  or  pans  again  and  again.  Recognizing  these  difficulties,  it 
was  stated  at  the  outset  of  the  Ivanhoe  experiments  that  all 
that  product  which  passed  a  150-mesh  would  be  called  'slime,' 
whether  it  came  from  a  tube -mill  or  grinding  pan.  As  some  basis 
had  to  be  made  for  comparison,  this  was  thought  to  be  the  fairest 
and  the  returned  slime  which  causes  Mr.  James  so  much  worry 
is  in  reality  very  fine  sand.  In  the  Ivanhoe  report  the  eturn 
feed  is  spoken  of  in  every  instance  as  'sand,'  and,  as  shown,  both 
tube-mill  and  pans  had  their  complement  of  it.  If  in  place  of 
writing  contradictory  statements,  Mr.  James  would  set  him- 
self the  task  of  defining  what  slime  is,  and,  having  satisfied  the 
mining  community  on  that  point,  he  then  invents  some  simple 
appliance  which  would  eliminate  that  slime,  and  only  sends  back 
to  be  re-ground  that  part  which  according  to  his  definition  re- 
quired it,  then  perhaps  further  trials  may  be  undertaken  between 
grinding  machines  that  would  satisfy  even  the  most  critical. 

The  fact  of  the  Ivanhoe  tests  being  checked  by  a  tube-mill 
expert  sent  by  Messrs.  Bewick,  Moreing  &  Co.,  from  the  Oroya 
Brownhill  mine,  is  sufficient  to  remove  any  chance  of  bias  on  the 
part  of  those  responsible  for  the  figures  given. 

Coming  now  to  the  cost  allowed  for  flints  and  liners — which 
Mr.  James  remarks  as  being  excessive  —  I  can  only  state  that 
the  costs  shown  were  based  on  the  consumption  experienced  dur- 
ing the  progress  of  the  experiments  and  which  agreed  closely 
with  results  obtained  on  a  large  scale  on  neighboring  mines,  and 
that,  as  shown  later  on,  the  longevity  of  liners  in  the  Kalgoorlie 
district  is  unique.  Leaving  out  the  difference  in  wear  and  tear 
of  working  parts,  the  question  of  a  pan  being  superior  to  a  tube- 
mill  in  breaking  down  coarse  sand  is  so  evident  that  it  is  hardly 
worth  discussing. 

It  comes  as  a  surprise  to  those  unacquainted  with  fine -grind- 
ing operations  at  Kalgoorlie  that  iron  liners  should  still  be  in 
use,  but  when  we  consider  the  records  put  up  there  on  hard  sul- 
phide ore,  one-inch  iron  liners  lasting  from  four  to  six  months, 
or  longer  than  three-inch  silex  liners  do  on  the  Rand,  it  is  perhaps 
no  wonder  that  Kalgoorlie  metallurgists  are  reluctant  to  discard 
such  a  useful  friend.  The  reason  for  the  great  difference  in  wear 
in  liners  between  two  such  important  mining  centres  is  worthy 
of  careful  investigation.  From  knowledge  of  both  Kalgoorlie 
and  Rand  practice  I  would  say  that  the  sand  of  the  latter  place 


194  RECENT  CYANIDE  PRACTICE. 

is  much  sharper,  and  also  the  fact  that  the  product  entering  the 
tube -mills  on  the  Rand  is  coarser  on  account  of  it  practically 
only  passing  through  once,  while  Kalgoorlie  mills  in  grinding  to 
a  slime  have  a  large  percentage  of  original  feed  returned  again  and 
again,  and  in  consequence  the  feed  entering  them  is  much  finer. 
Another  peculiar  circumstance  is  that,  while  it  is  difficult  on  the 
Rand  to  find  a  tube-mill  under  22  ft.  in  length,  in  the  whole  of 
Western  Australia  there  is  no  mill  over  16  ft.,  the  majority  being 
but  13  ft.  long! 

A  practical  proof  of  the  esteem  in  which  grinding  pans  are 
held  is  that  about  200  are  now  engaged  in  Western  Australia, 
40%  of  this  total  in  grinding  raw  sand,  admittedly  not  to  a  slime, 
for  those  mines  which  are  sliming  their  total  product  had  tube- 
mills  erected  or  on  order  before  the  remarkable  grinding  ability 
of  pans  was  recognized;  but  where  it  has  been  decided  to  increase 
the  capacity  of  these  latter  plants,  pans  have  invariably  been  in- 
stalled in  preference.  It  is  perhaps  worthy  of  notice  that  about 
a  dozen  have  also  arrived  or  are  on  their  way  to  South  Africa. 

It  is  a  matter  of  sincere  pleasure  to  those  responsible  if  in 
the  smallest  degree  the  increased  use  of  grinding  pans  has  been 
due  to  the  Ivanhoe  experiments,  and  also  the  recommendation 
to  millmen  of  a  grinding  machine  that  (to  use  Mr.  James'  own 
words)  has  the  advantages  over  tube-mills  of  ''using  less  horse- 
power per  unit,  their  greater  convenience  in  working,  their  capac- 
ity for  amalgamation,  the  granular  (?)  nature  of  their  product," 
and  it  may  be  added  (until  demonstrated  otherwise)  their  un- 
doubted superiority  in  breaking  down  coarse  sand,  and  their 
more  than  equal-  success  in  sliming. 

H.  T.  BRETT. 

Sabiwa  Mine,  Gwanda,  Rhodesia,  October  4. 


CYANIDE  PRACTICE  AT  KALGOORLIE 

(December  29,  1906) 

The  Editor: 

Sir — With  reference  to  Mr.  Brett's  long  letter  in  your  issue 
of  December  22,  of  which  you  kindly  sent  me  an  advance  proof, 
I  notice  that  in  spite  of  the  space  at  his  command  Mr.  Brett  does 
not  apparently  deny  my  suggestion  that  in  his  so-called  tube -mill 
versus  pan  tests  he  actually  fed  into  the  tube-mill  with  the  sand 
to  be  re-ground  more  slimed  (finished)  product  than  sand  to  be 
re-ground,  although  he  must  have  known  that  such  a  procedure 
would  seriously  diminish  the  duty  of  the  tube -mill. 

As  Mr.  Brett  does  not  deny  this,  his  long  personal  explana- 
tion calls  for  no  other  comment  from  me ;  but  I  would  like  to  add 
that  the  pan  work  at  the  Ivanhoe  has  impressed  me  so  favorably 
that  were  I  laying  down  an  installation  of  pans  I  should  deem 
myself  fortunate  if  able  to  secure  the  services  of  Mr.  Brett  for 
this  purpose — so  efficiently  have  the  pans  been  worked  at  his 
late  mill  at  Kalgoorlie. 

ALFRED  JAMES. 
-      London,   December  5. 


PROGRESS  IN  CYANIDATION  DURING  1906 

BY  ALFRED  JAMES 

(January  5,  1907) 

The  making  of  slime  and  the  treatment  of  it  may  be  taken 
as  the  main  directions  of  improvement  in  cyanidation  during  the 
year.  The  use  of  tube-mills  has  progressed  by  leaps  and  bounds, 
and ;  is  now  rapidly  becoming  well-nigh  universal,  but  with  the 
adoption  of  these  machines  the  question  of  slime  treatment  has 
forced  itself  into  still  greater  prominence,  and  as  stated  by 
me  last  year,  some  of  our  keenest  metallurgists  have  been  at- 
tacking this  problem,  and  it  is  now  possible  to  state  that  their 
endeavors  have  met  with  a  considerable  measure  of  success. 

As  will  be  indicated  later,  progress  has  also  been  made  in  the" 
treatment  of  difficult  ores — including  silver-gold  ores,  antimony- 
gold  concentrate,  and  cupriferous  tailing — and  in  crushing,  roast- 
ing, and  conveying  we  are  ahead  of  last  year's  practice. 

It  is  interesting  to  note  how  the  treatment  of  gold  ores  has 
overlapped  the  metallurgy  of  the  other  metals.  Fine  sliming 
and  prolonged  cyanide  treatment  constitute  a  method  that,  in 
many  cases,  is  ousting  chloridizing  roasting  and  the  old  patio 
process  for  the  treatment  of  silver  ores.  Copper  ore  in  Chile  is 
now  being  leached  in  a  cyanide  plant — without  cyanide — and  the 
Merton  roaster,  so  successfully  introduced  in  Australia  for  gold 
ores  has  taken  a  hold  on  the  zinc  industry  for  the  roasting  of  zinc 
blende,  and  for  the  treatment  of  the  zinc-lead-silver  concentrate 
of  Broken  Hill.  Indeed  one  cannot  fail  to  be  struck  by  the  way 
in  which  names  well  known  in  gold-milling,  such  as  Argall,  Marri- 
ner,  and  Simpson,  have  been  attracted  to  the  problems  presented 
by  zinc-lead  ores. 

It  is  difficulty  to  put  a  finger  on  any  one  part  of  the  world 
as  having  made  the  most  striking  progress  of  he  year.  Western 
Australia  still  has  the  pre-eminence.  Inventions  that  may  have 
originated  in  other  countries  appear  to  be  more  quickly  put  to 
definite  practical  service  there  than  elsewhere,  and  just  as  Western 
Australia  has  taken  the  lead  in  fine  sliming  and  in  circulating 
cyanide  solutions  through  the  mill,  so  now  it  seems  to  be  the  pio- 
neer in  slime  treatment.  Probably  the  emulation  arising  from 


PROGRESS  IN  CYANIDATION  DURING  1906.        197 

the  up-to-date  methods  of  the  leading  firm  of  mining  engineers 
on  the  one  hand,  and  independent  managers  on  the  other  hand,  has 
tended  to  place  Western  Australia  in  the  forefront  in  the  matter 
of  new  methods,  high  extractions,  and  low  costs.  Certainly  such 
men  as  Hamilton,  Moss,  Nicholson,  and  Klug,  and  the  gentlemen 
associated  with  Bewick,  Moreing  &  Co.,  have  cause  for  congratu- 
lation on  the  results  they  have  achieved  and  are  achieving,  and 
the  adoption  of  their  methods  in  other  regions  shows  that  the 
industry,  not  locally  but  generally,  is  under  an  obligation  to  them, 
as  well  as  to  the  alert  and  progressive  West  Australian  Chamber 
of  Mines,  which  has  published  an  excellent  series  of  articles  by 
Mr.  Robert  Allen  on  ore  treatment  as  carried  out  at  the  various 
local  installations. 

American  practice  has  chiefly  busied  itself  with  tube-mills 
and  slime  treatment.  Argall,  Bosqui,  Butters,  and  Merrill  have 
all  been  contributing  to  our  advancement  by  getting  out  im- 
proved methods.  In  Africa  the  publication  of  the  results  ob- 
tained by  the  brothers  Denny  at  the  Meyer  &  Charlton  and  New 
Goch  mills  has  caused  much  interest,  for  extraction  and  output 
have  been  increased  and  cost  lowered — mainly  by  the  use  of 
tube-mills.  Record  gold  outputs  are  again  being  produced  from 
the  Transvaal,  which  has  more  than  recovered  the  set-back  occas- 
ioned by  the  war. 

Crushing. — The  tendency  to  stage-crushing  is  in  still  greater 
evidence.  Coarse  breakers,  fine  crushers,  heavy  stamps,  pans, 
tube-mills,  are  not  an  uncommon  sequence.  With  reference  to 
breaking  of  ore,  however,  it  has  not  yet  been  proved  that  reduction 
to  finer  than  2J-in.  cube  is  advantageous  for  the  stamps.  Ex- 
periments seem  to  indicate  that  finer  crushing  is  more  expensive 
than  the  gain  arising  from  any  increase  in  stamp  duty  will  warrant. 

As  for  crushers,  the  Gates  type  still  holds  the  field  for  big 
work,  but  the  Bigelow  breaker,  of  the  Blake  type  but  with  the  pit- 
man working  in  compression  and  having  its  weight  assisting  the 
crushing  stroke,  appears  to  be  replacing  the  other  kinds  at  Kalgoor- 
lie,  and  to  show  a  lower  running  cost  than  either  the  gyratory  or 
the  older  reciprocating  patterns. 

Stamps  of  1,500-lb.  weight  are  now  in  use  on  the  Rand,  and 
it  looks  as  if  the  limit  of  weight  had  not  yet  been  reached.  But 
little  has  been  heard  this  year  of  anvil-blocks  for  mortars,  although 
at  the  Waihi  Grand  Junction  they  seem  to  have  made  for  a  con- 


198  RECENT  CYANIDE  PRACTICE. 

siderable  increase  in  output  beyond  that  originally  expected. 
Judging  by  out-put  per  horse-power,  ball-mills  would  appear  to 
be  the  most  efficient  machine,  with  an  output  of  over  two  tons 
per  h.p.  day  on  the  best  types,  crushing  all  the  ore  through  27 
mesh,  but  the  cost  of  dry-crushing  at  the  South  Kalgurli  appears 
to  be  about  three  shillings  per  ton  as  against  roughly  Is.  9d.  per 
ton  crushing  wet  at  the  Oroya-Brownhill,  Lake  View,  and  Ivanhoe. 
On  the  other  hand  the  latter  crush  through  very  much  coarser 
screening  (10,  17,  and  15  mesh,  respectively) ,  reducing  the  over- 
sized product  by  their  pans  and  tube-mills. 

Fine  Grinding. — The  tendency  has  been  to  use  stamps  for 
rough  crushing  only,  that  is,  to  substitute  coarser  screens  for  those 
formerly  in  use,  and  from  the  pulp  to  separate  the  coarse  product 
and  to  grind  it  in  tube-mills  or  pans.  There  have  been  no  notable 
contributions  to  our  knowledge  this  year  as  to  which  is  the  best 
appliance  for  this  purpose.  Tube-mills  seem  to  be  generally  em- 
ployed, except  at  Kalgoorlie,  where  the  roasted  ore  can  be  efficiently 
ground  to  the  required  fineness  in  pans.  Not  that  pans  are  not 
effective  on  raw  ore.  On  the  contrary,  the  Ivanhoe  results  show 
very  good  work  indeed,  and  it  is  to  be  much  regretted  that  the 
comparative  tests  made  at  that  mine  between  pans  and  tube- 
mills  were  carried  out  in  such  a  way  as  to  make  the  results  worse 
than  useless.  But  it  is  a  matter  for  serious  thought  that  the  Ivan- 
hoe costs  for  re-grinding  sand  should  be  only  8^d.  per  ton  treated, 
when  the  Oroya-Brownhill,  Lake  View,  and  other  mills  should 
show  a  figure  twice  as  high.  It  cannot  well  be  a  matter  of  pans 
only,  or  we  should  have  heard  of  similar  low  results  from  the  other 
companies  exclusively  employing  pans  (at  the  Oroya  and  Lake 
View  pans  are  used  in  conjunction  with  tube-mills).  Is  it  that 
the  Ivanhoe  ore  is  softer  or  that  the  final  product  is  not  slimed  as 
fine?  The  management  has  recently  been  very  keen  on  reducing 
the  value  in  their  residue — and  have  succeeded  in  doing  so  materi- 
ally— and  one  would  therefore  expect  that  they  would  not  over- 
look the  gain  from  crushing  as  fine  as  their  neighbors.  It  is  to 
be  assumed,  therefore,  that  the  crushing  is  as  fine,  but  the  fact 
remains  that  the  cost  of  grinding  sand  at  the  Ivanhoe  is  less  than 
half  that  of  neighboring  companies  of  the  same  group  that  employ 
wet  crushing.  There  is  an  obvious  need  of  that  careful  compara- 
tive test  between  pans  and  tube-mills  for  which  I  have  so  often 
asked  and  which  I  hoped  would  be  undertaken  by  Klug  or 


PROGRESS  IN  CYANIDATION  DURING  1906.        199 

Denny.  Indeed,  it  was  understood  that  the  latter  was  making 
such  tests,  but  nothing  seems  to  have  come  of  them. 

Meanwhile  I  am  informed  that  such  a  test  has  been  made 
at  Broken  Hill  with  a  pan,  a  wet-grinding  ball-mill,  a  disc-grinder, 
and  a  tube-mill,  and  that  the  tube  has  proved  itself  the  best  of  the 
lot,  but  in  the  absence  of  details,  we  can  only  take  this  statement 
as  the  expression  of  individual  opinion.  Even  if  we  assume 
tube-mills  to  be  the  best  slime-makers  there  is  still  the  question  of 
stage-grinding,  and  it  is  by  no  means  certain  that  the  preliminary 
crushing  of  the  coarser  particles  could  not  be  effected  more  econom- 
ically in  pans. 

The  best  pan  figures  have  been  given  above.  The  following 
tube-mill  data  will  prove  of  interest.  African  costs  have  been 
reduced  from  8^d.  (per  ton  ground)  down  to  5Jd.,  of  which  1.89d. 
is  for  power,  0.7d.  for  pebbles,  and  0.93d.  for  liners.  Mr.  Henry 
Leupold  states  that  silex  linings  are  half  the  cost  and  last  two  and 
a  half  times  as  long  as  iron  liners.  The  Consolidated  Gold  Fields, 
made  careful  tests  on  manganese  steel  liners  as  against  silex 
with  the  result  that  the  former  were  shown  to  be  more  expensive 
and  the  grinding  nothing  like  as  good,  owing  to  the  slipping  of 
the  pebbles  caused  by  the  polished  surface  of  the  manganese 
steel.  At  El  Oro,  a  20-ft.  mill  with  7£  tons  of  pebbles  grinds 
125  tons  per  day  of  sand  for  60  h.p.  to  such  a  fineness  that  90% 
will  pass  100-mesh  and  50%  a  200-mesh  screen.  At  Waihi,  an 
18-ft.  mill  grinds  77  tons  of  20-mesh  sand  per  day,  so  that  93% 
will  pass  150-mesh,  for  37J  h.p.  The  Waihi  is  notorious  for  the 
hardness  of  its  ore,  which  ball-mills  failed  to  grind  satisfactorily. 
Their  tube-mills  do  not  appear  to  be  run  to  their  utmost  capacity, 
but  their  figures  are  interesting  as  an  example  in  practice  of  direct 
tube-mill  work,  that  is,  without  any  return  of  material  treated. 
The  above  figures,  of  over  two  tons  slimed  per  horse-power,  at  first 
sight  show  a  less  duty  than  that  mentioned  by  me  a  year  ago, 
of  four  tons  per  horse-power  in  Africa,  but  it  must  be  remembered 
that  the  African  crushing  was  much  coarser,  they  having  at  that 
time  adopted  a  standard  of  under  two  per  cent  retained  on  60-mesh. 

But  apart  from  the  question  of  comparative  cost  of  work  done, 
tube-mills  have  shown  their  distinct  economical  advantage  as  well 
as  their  capacity  for  re-grinding.  Reference  was  made  last  year 
to  the  huge  additional  net  profit  of  £65,000  per  year  accruing 
to  the  El  Oro  Company  from  this  source.  At  Waihi  three  18-ft. 


200  RECENT  CYANIDE  PRACTICE. 

tube-mills  and  90  stamps  have  increased  the  output  from  2.89  tons 
per  stamp  per  day  to  four  tons,  and  have  lessened  the  value  of 
the  residue  by  50%.  They  have  improved  the  extraction  by 
amalgamation  from  5  to  7%,  and  effected  a  75%  saving  in  screening. 
They  find  also  that  since  the  adoption  of  tube-mills  the  slime 
is  more  permeable  and  the  filter-press  charges  take  less  time  for 
treatment,  so  that  the  same  presses  can  now  deal  with  30%  more 
slime  than  before.  The  new  Barry  linings,  made  on  the  spot, 
seem  to  be  most  effective  and  to  result  in  a  great  saving  of  cost 
over  the  imported  silex.  One  set  of  linings  is  stated  to  last  for 
six  months,  and  a  new  set  is  always  kept  ready  at  hand  and  can  be 
replaced  in  two  days.  Mr.  H.  P.  Barry  makes  a  great  point  of 
having  his  linings  as  rough  as  possible,  so  as  to  give  a  grip  to  the 
pebbles,  and  has  modified  his  doors  to  effect  this  also. 

At  Johannesburg  Mr.  W.  R.  Bowling  emphasizes  the  necessity 
for  the  complete  separation  of  the  sand  to  be  re-ground  from  the 
slime  in  the  mill-pulp,  and  for  keeping  the  proportion  of  water 
to  sand  at  as  low  a  figure  as  possible.  He  shows  at  the  Robinson 
Deep  a  0.48  dwt.  lower  residue  (formerly  1.26  dwt.,  now  after 
tube-mill  treatment  0.78  dwt.),  and  an  increased  capacity  of  2,300 
tons  per  month.  The  Eckstein  mines,  in  addition  to  the  increased 
output  resulting  from  the  tube-mills,  show  an  additional  profit 
of  from  Is.  to  Is.  6d.  per  ton  (Is.  at  the  Robinson,  Is.  4d.  at  the 
Ferreira)  resulting  from  the  increased  extraction,  which  has  lessened 
the  value  of  the  residue  by  about  half  a  pennyweight.  There 
are  now  58  tube-mills  at  work  on  the  Rand — and  more  on  order — 
at  24  different  mines,  and  these  58  tubes  at  the  24  mines  only  have 
increased  the  amalgamation  returns  of  the  whole  of  the  Rand  by 
three  per  cent. 

At  present  the  Knight's  Deep  appears  to  have  the  highest 
monthly  output  per  stamp — for  complete  battery — of  7.68  tons 
per  stamp,  since  reduced  by  the  substitution  of  different  screening 
to  6.68  tons.  In  Western  Australia  the  Oroya-Brownhill  crushes 
7J  tons  per  stamp  through  a  10-mesh  screen,  and  the  Great  Fingall 
(1,150-lb.  stamps)  exhibits  an  average  duty  of  seven  tons  per 
24  hours  through  a  12-mesh  screen,  and  the  Sons  of  Gwalia  at 
Leonora  (1,000-lb.  stamps)  treats  6.68  tons  per  head  per  day 
through  20-mesh  screening. 

It  is  estimated  that,  in  addition  to  the  gains  already  mentioned 
as  resulting  in  Africa  from  the  use  of  tube-mills,  there  is  a  saving 


PROGRESS  IN  CYANIDATION  DURING  1906.         201 

of  30%  in  equipment  arising  from  the  adoption  of  them  in  place  of 
obtaining  the  same  output  by  the  addition  of  the  increased  number 
of  stamps  necessary.* 

Amalgamation. — The  increased  extraction  by  amalgamation 
resulting  from  the  use  of  tube-mills,  has  been  referred  to  already. 
At  Waihi,  amalgamation  is  carried  out  on  plates  set  in  a  large 
building  apart  from  the  mill,  sand  and  slime  being  treated  sep- 
arately. There  is  much  to  be  said  for  this  arrangement.  Companies 
circulating  cyanide  solutions  through  the  mill  find  a  scouring 
of  their  copper  plates  by  the  cyanide  solutions.  Denny,  at  the 
Meyer  &  Charlton,  proposed  to  minimize  this  action  if  possible 
by  adopting  shorter  plates,  but  probably  the  better  method  would 
be  to  exclude  copper  plates  from  the  amalgamation  apparatus. 
At  the  Lake  View  (Kalgoorlie),  for  instance,  plates  are  discarded 
and  amalgamation  takes  place  in  pans;  in  that  mill  51%  of  the 
value  of  the  concentrate  is  recovered  by  amalgamation  and  46% 
by  subsequent  cyanidation. 

Roasting. — Thomas  Edwards  has  increased  the  capacity 
of  his  recent  furnaces  by  a  parallel  system  of  rabbles,  which  is 
stated  to  promote  inter-rabbling.  G.  C.  Klug  has  adopted  this 
for  the  Holthoff-Wethey  furnaces  at  the  Perseverance,  and  claims 
high  results.  Merton  has  also  modified  his  furnace  by  making  it 
a  five-hearth  roaster,  and  also  of  greater  hearth-area.  The  great 
Boulder  Proprietary  has  a  roasting  cost  of  2s.  3d.  per  ton  (employing 
Merton  furnaces)  reducing  an  ore  going  4  to  5%  sulphur  down 
to  0.07%  sulphur,  as  sulphide;  with  this  exception  the  record  of 
the  South  Kalgurli  type  of  Merton  furnaces  does  not  yet  appear 
to  have  been  improved  on,  either  for  cost  (2s.  6d.  per  ton  roasted), 
output  (32  tons  per  diem  for  small-size  furnace,  taking  1J  h.p.), 
or  efficiency  (3.1%  sulphur  down  to  0.01%  sulphur  as  sulphide; 
one  ton  of  green  wood  roasting  11  tons  of  ore).  With  regard  to 
the  suggestion  that  I  made  in  this  review  a  year  ago  of  adding, 
say,  two  pounds  of  lead  acetate  per  agitator  charge  (40  to  60  tons) 
of  roasted  ore,  Richard  Hamilton  of  the  Great  Boulder  finds 
that  the  use  of  lead  salts  appears  to  result  in  an  increased  con- 
sumption of  zinc  in  the  precipitation  boxes,  as  against  which 
he  benefits  by  a  saving  of  roasting  fuel,  an  increased  tonnage 
through  the  mill  for  the  same  labor,  a  reduction  in  the  value  of  the 


*  South  African  Mines,  October  27,  1906. 


202  RECENT ^CYANIDE  PRACTICE. 

residue,  and  a  general  feeling  of  confidence  in  the  ability  to  set  foul 
roasts  all  right  quickly  in  spite  of  fluctuations  in  natural  draft. 

Concentration. — There  appears  to  be  no  great  advance  made 
this  year  in  the  concentration  of  gold  ores.  The  difficulty  remains 
that  an  attempt  to  concentrate  out  refractory  particles  from  an 
ore  usually  leaves  a  tailing  practically  as  refractory  as  the  original 
ore. 

It  was  hoped  that  fine  sliming  and  the  Wilfley  slime-table 
might  overcome  this  difficulty,  but  the  latter  machine  is  by  no 
means  perfect  and  maintenance  is  a  most  formidable  item.  So 
far  the  old  canvas  tables  or  frames  appear  to  give  the  best  results, 
but  the  cost  of  washing  down  is  very  heavy  indeed — amounting 
in  certain  cases  to  30s.  or  40s.  per  ton  of  concentrate  produced. 
A  continuous  rough  rubber  or  canvas-belt  table,  somewhat  on  the 
Luhrig  or  Buss  system,  might  solve  the  difficulty,  though  the 
capacity  per  unit  would  necessarily  be  small;  or  the  old  treatment 
table  could  have  a  traveling  system  of  washing  pipes  worked  by  a 
water  balance,  and  thus  avoid  the  expense  of  so  much  boy-labor. 

The  flotation  processes  are  being  mainly  applied  to  zinc-lead 
concentrate  at  Broken  Hill,  rather  than  gold  ores.  De  Bavay 
and  Simpson  appear  to  have  made  an  interesting  discovery  as  to 
the  principles  involved  in  the  various  flotation  processes,  which 
they  claim  depend  on  the  surface  tension  of  sulphides  as  con- 
trasted with  the  gangue,  the  greasy  sulphides  when  wetted  retaining 
an  envelope  of  air  that  is  expanded  by  heat,  or  by  vacuum,  or 
aided  by  the  air  entangled  in  oil,  or  gelatinous  silica,  or  by  flowing 
the  mineral  pulp  in  very  thin  layers — practically  all  surface — 
over  inclined  tables. 

Treatment  of  Difficult  Ores. — Cupriferous  tailing  with  a  copper 
content  not  exceeding  0.5%  is  now  successfully  treated  by  leaching 
out  the  copper  with  dilute  sulphuric  acid  and  precipitating  on 
scrap  iron,  as  described  by  W.  S.  Brown. f  With  ores  containing 
more  copper — but  not  rich  enough  to  smelt — a  preliminary  roasting 
of  the  ore  has  been  found  to  improve  matters.  The  addition  of 
ammonia  to  the  cyanide  solution  has  been  previously  suggested 
and  carried  out  in  practice. 

Auriferous  antimonial  concentrate,  containing  say  20% 
antimony  and  arsenic,  has  been  successfully  treated  by  an  ordi- 


t Proceedings  Institution  of  Mining  &  Metallurgy,  190G. 


PROGRESS  IN  CYANIDATION  DURING  1906.        203 

nary  careful  roast  of  the  ore  previously  mixed  with  from  2  to  5% 
charcoal  or  coal,  followed  by  a  hot  acid  wash  of  dilute  hydro- 
chloric acid  (obtainable  by  exposing  old  chlorine  solutions  to 
direct  sunlight),  and  then  lixiviating  with  cyanide  or  chlorine.  A 
variation  successfully  employed  is  to  roast  as  above,  add  salt  at 
the  end  of  the  roast,  and  chlorinate.  Both  methods  have  yielded 
90%  extractions,  but  have  the  draw-back  of  requiring  very  care- 
ful roasting. 

Slime  Treatment. — The  brothers  Denny  have  made  something 
of  a  sensation  at  Johannesburg  by  the  methods  they  have  applied 
at  their  new  plants.  In  these  they  have  adopted  the  West  Austra- 
lian method  of  circulating  dilute  cyanide  solutions  through  the 
mill  and  filter-pressing  their  slime  in  Dehne  hydraulic-closed  filter- 
presses.  They  claim  a  recovery  of  over  94%  at  a  treatment 
cost,  including  cyanide,  filter-pressing,  and  disposal  of  residue 
(5d.),  of  Is.  lOd.  per  ton.  As  this  carrying  into  practice  of  their 
proposed  treatment  scheme  was  not  effected  without  many  proph- 
ecies of  failure,  and  as  the  cost  of  the  installation  necessary 
appears  to  be  less  than  half  that  of  the  method  of  treatment 
locally  in  vogue,  it  is  natural  that  their  work  should  have  received 
much  attention,  and  as  their  figures  do  not  seem  to  be  seriously 
contested,  the  Denny  brothers  certainly  look  like  scoring  heavily 
again  as  the  result  of  their  enterprise  and  foresight,  just  as  they  did 
previously  by  the  introduction  on  the  Rand  of  tube-mills. 

But  perhaps  the  two  greatest  successes  in  slime  treatment — 
as  being  a  real  advance  on  established  filter-press  practice — are 
the  respective  methods  evolved  by  Ridgway  at  the  Boulder  and 
by  Barry  at  Waihi.  Anyone  reading  Mr.  R.  Oilman  Brown's 
article*  on  the  Moore  filter,  must  have  noticed  the  very  sloppy, 
badly  arranged  frames  shown  in  the  illustrations.  We  can  under- 
stand, perhaps,  from  these  illustrations,  one  of  the  reasons  for  the 
small  success  attending  the  Moore  filter  in  America.  At  Waihi, 
Barry  has  a  frame^f  which  is  much  more  effective  than  that  shown 
in  the  description  referred  to  above,  and  he  has  successfully  treated 
many  thousands  of  tons  by  his  method  of  open-framed  atmos- 
pheric filtration;  but  the  drawback  to  this — as  to  the  Moore  bas- 
ket-filter— is  the  necessity  of  having  men  constantly  in  attendance 
to  clean  the  frames. 

*MINING  AND  SCIENTIFIC  PRESS,  September  8,  1906. 
f  The  Mining  Journal,  September  30,  1906. 


204  RECENT  CYANIDE  PRACTICE. 

Charles  Butters  seems  to  have  been  alive  to  the  defects  of 
the  Moore  frame,  and  has  got  out  one  that  he  appears  to  be  working 
with  considerable  success  at  Virginia  City,  as  does  also  F.  L.  Bosqui 
at  Tonopah.  Butters,  however,  has  apparently  allied  himself 
to  the  Cassel  enclosed  type  of  press,  which  looks  similar  to  that 
referred  to  in  a  previous  paper  as  being  experimented  with  at 
Johannesburg  unsuccessfully. 

The  Ridgway  machine  has  now  been  in  use  for  a  year  at 
the  Great  Boulder,  and  has  treated  some  thousands  of  tons  of 
slime  quite  automatically  and  without  any  continuous  supervision, 
and  Hamilton,  who  has  been  testing  it  alongside  his  filter-press 
installation,  is  so  satisfied  with  the  results  that  he  is  laying  down  a 
plant  to  treat  500  tons  per  day — the  largest  slime  plant  in  the  south- 
ern hemisphere.  The  principle  of  the  machine  is  a  number  of 
horizontal  plates  revolving  round  a  central  vertical  post,  which  is 
really  a  tube,  and  to  which  pipes  communicating  with  each  plate 
are  attached.  Each  plate  has  an  under-filtering  surface,  and 
through  a  portion  of  its  revolution  it  dips  into  the  slime-pulp. 
A  cake  is  formed  by  the  application  of  a  vacuum,  and  the  plate  in 
the  course  of  its  journey  around  its  axis  finds  itself  next  in  a  water 
bath,  where  it  remains  sufficiently  long  for  thorough  washing. 
The  cake  is  then  dislodged  automatically  into  the  residue  deposit 
system.  This  machine  is  certainly  cheaper  than  the  filter-presses, 
both  in  first  cost  and  in  operation,  and  an  equipment  to  do  the  duty 
of  an  African  decantation  plant  should  not  only  yield  higher 
recoveries  at  a  lower  working  cost,  but  should  be  installed  for  less 
than  half  the  expense  of  the  existing  system. 

Of  the  other  methods  referred  to  last  year  but  little  has  been 
heard.  C.  W.  Merrill  appears  to  be  still  at  work  on  his  hydraulic 
emptying  filter-press,  but  details  of  successful  work  have  not  yet 
reached  me.  Philip  Argall  has  a  fixed  frame  and  movable  tank, 
but. appears  too  busy  at  Cripple  Creek  to  be  able  to  give  much 
attention  to  his  slime-filter  for  the  present. 

In  Western  Australia  one  of  the  groups  had  a  method  of 
upward  percolation  of  the  solutions  through  the  slime-pulp  during 
agitation,  but  this  method  does  not  appear  to  have  been  attended 
with  any  great  success.  Generally  speaking,  it  looks  as  if  some 
direct  method  of  automatic  atmospheric  filtration  would  displace 
both  decantation  and  Dehne  filter-pressing,  although  at  the  outset 
it  will  probably  require  a  higher  degree  of  intelligence  for  its  effec- 
tive and  successful  working. 


PROGRESS  IN  CYANIDATION  DURING  1906.       205 

Re-treatment  of  Tailing. — Not  much  has  been  said  of  the  Stark 
process  during  the  year.  It  seems  to  have  been  most  profitably 
applied  to  the  Crown  Reef  dump.  Is  it  that  there  is  any  special 
characteristic  feature  of  this  dump  that  makes  it  suitable  for  the 
Stark  process  ? 

Mercuric  Cyanide. — A  reference  to  a  test  by  Butters,  on  El 
Oro  ore,  of  a  mercury  salt  added  to  the  cyanide  solution,  recalls 
the  investigation  made  by  the  Cassel  company  (the  owners  of  the 
caynide  patents)  in  1895  into  the  use  of  this  salt.  They  obtained 
improved  results,  on  some  ores,  of  3J%  greater  extraction  of  the 
gold  and  3%  greater  extraction  of  the  silver,  with  a  lower  consump- 
tion of  cyanide,  but  the  tests  were  not  continued,  as  the  improved 
extractions  seemed  insufficiently  encouraging  in  view  of  the  addi- 
tional expense  of  the  added  salt;  but  Butters'  tests  have  renewed 
interest  in  the  subject,  and  we  hope  for  fuller  data. 

Costs. — Tube-milling,  fine  grinding,  milling,  and  roasting 
costs  have  been  given  above.  The  following  tabulated  statement 
of  West  Australian  costs  will  show  the  progress  still  being  made 
in  that  region  by  comparison  with  those  in  preceding  papers,  as 
well  with  those  obtaining  elsewhere : 

Rock-Breaking. 

Mill.  Pence. 

Lake  View 1.71 

Ivanhoe 1 . 87 

South  Kalgurli  (dry) 3 . 39 

Milling. 

Lake  View Is.  9d. 

Ivanhoe Is.  9d. 

South  Kalgurli  (dry) 2s.lld. 

Concentrating. 

Lake  View 6s.  7d.  per  ton  concentrated 

9d.  per  ton  milled 

Ivanhoe 8s.  Od.  per  ton  concentrated 

lOd.  per  ton  milled 

Roasting. 

Lake  View 3s.  lOd.  per  ton  roasted  (concentrate  only) 

Ivanhoe 5s.  5d. 

South  Kalgurli 2s.  6d.  (all  the  ore) 

Great  Boulder  Proprietary     2s.  4d.         " 

Fine  Grinding  Sand. 

Lake  View Is.  lOd.  per  ton  ground 

Ivanhoe 8d. 

South  Kalgurli Is.     3d.       " 


206  RECENT  CYANIDE  PRACTICE. 

Cyaniding  by  Agitation. 

Lake  View 3s.  Id.  (includes  Is.  4d.  for  KCy  and   Is.   2d.  for  BrCy) 

Ivanhoe 4s.  Id.  (includes  lid.  KCy,  2s.  6d.  BrCy,  and  royalty  2d.) 

South  Kalgurli, Is.  4d (includes  7d.  KCy.) 

From  the  above  it  appears  that  the  agitation  treatment, 
less  cyanide  and  bromo-cyanide,  but  including  power,  lime,  labor, 
and  supplies,  costs  roughly  7d.  per  ton  (Ivanhoe.Gd.). 

Cyaniding  by  Percolation. 

Ivanhoe 2s.  2d.     (including  9d.  for    KCy  and  lime) 

Great  Fingall. ll^d.      (including  6d.  for    KCy  and  lime) 

Filter-Pressing. 

Lake  View Is.  7d. 

Ivanhoe Is.  6d. 

South  Kalgurli Is.  6d.  per  ton  filter-pressed. 

The  cost  of  filter-cloths  at  the -Lake  View  Consols  has  been 
under  £d.  per  ton  pressed  for  every  month  this  year,  save  once  when 
it  was  under  f  d. 

Total  Treatment  Costs. 

Ivanhoe 9s.     Od. 

South  Kalgurli 11s.     3d. 

Great  Boulder  Proprietary  ...    11s.     6d. 

Great  Fingall 6s.  lid. 

Sons  of  Gwalia 5s.     2d.  per  ton  treated. 

General. — The  battle  of  the  processes  at  Kalgoorlie  is  now  over. 
It  is  admitted  that  the  all-roasting  process  gives  the  most  profit- 
able extraction,  but  the  good  fight  made  by  the  wet-crushing 
bromo-cyanide  party,  and  notably  by  the  Ivanhoe,  has  been  of 
the  greatest  service  to  the  industry,  and  the  Ivanhoe's  costs  are  such 
as  to  reflect  great  credit  on  the  management  and  the  staff;  but  the 
fine  showing  made  by  the  South  Kalgurli,  the  Great  Boulder, 
the  Kalgurli,  and  other  companies,  appears  now  to  have  convinced 
even  the  former  advocates  of  bromo-cyanide. 


TUBE-MILL  LINING 

(January  5,  1907) 

The  Editor: 

Sir- — I  was  very  much  interested  in  Mr.  Drucker's  experiences 
with  tube-mill  linings  in  Korea,  as  described  in  your  issue  of  Novem- 
ber 17,  and  thought  a  few  notes  from  our  experience  of  the  past  two 
years  at  Bodie,  California,  might  add  a  point  or  two. 

The  tailing-flow  from  the  stamp-mill  of  the  Standard  Con. 
Mining  Co.,  passes  directly  through  classifiers.  The  tube-mill 
is  used  to  re-grind  the  underflow,  or  coarser  material  from  the  classi- 
fiers; with  which  is  also  fed  dry  tailing  from  the  old  slum  ponds. 
The  tube-mill  used  is  an  Allis- Chalmers  pattern,  about  22  ft.  long 
by  5  ft.  diam.,  as  illustrated  by  the  accompanying  photograph. 

The  first  lining  used  in  the  mill  consisted  of  special  steel 
plates  about  10  by  12  in.  area  by  one  inch  thick,  with  a  base  made 
so  that  the  entire  lining  was  intended  to  be  interlocking.  These  plates 
had  a  life  of  four  or  five  months,  but  as  is  often  the  case  with  cast- 
ings subjected  to  grinding  action,  some  of  them  would  wear  un- 
evenly and  occasionally  one  would  drop  out  of  place.  This  neces- 
sitated stopping  the  mill  and  replacing  the  loosened  plates. 

The  next  lining  used  was  in  the  form  of  pine  blocks,  cut  from 
4  by  6  in.  sawed  timber  into  6-in.  lengths,  trimmed  slightly  wedge- 
shaped  (to  allow  for  curvature  of  shell),  and  set  on  end.  To  place 
a  new  set  of  these  pine-block  liners,  including  removal  of  old  blocks, 
and  shoveling  out  and  in  of  the  load  of  pebbles,  required  usually 
about  36  hr.  (The  tube  has  only  one  man-hole,  the  cover  of  which 
is  shown  in  the  photograph.)  A  set  of  these  liners  lasted  from  10 
days  to  two  weeks.  Aside  from  its  short  life,  this  lining  had  the 
disadvantage  (by  reason  of  the  vegetable  oils  contained)  of  making 
a  soapy  mixture  with  the  alkalies  present  in  the  cyanide  solution 
(crushing  being  done  in  solution) .  This  saponification  caused  ex- 
cessive foaming  in  the  batteries  and  on  the  plates  of  the  stamp-mill 
(for  after  going  through  the  zinc-boxes  the  solution  was  re-standard- 
ized and  returned  to  the  battery  storage  vat) ,  and  also  in  the  tube- 
mill,  launders,  and  vats  in  the  cyanide  plant.  After  a  few  sets 
of  these  pine  liners  had  been  tried,  a  similar  set  was  made  out  of 
blocks  of  mountain  mahogany,  a  dense,  hard  wood  from  the  Sierra 
Nevada  mountains.  This  gave  a  few  days  longer  life,  and  the  saponi- 
fication was  decreased. 


208  RECENT  CYANIDE  PRACTICE. 

Next  we  tried  a  quartz  lining  similar  to  the  one  Mr.  Drucker 
describes,  except  that  there  were  no  steel  rails  on  the  inside  of  the 
shell.  The  quartz  consisted  of  selected  pieces  of  chalcedonic 
vein-stuff,  very  hard  and  close-grained,  from  the  mine.  This 
lining  was  carefully  put  in  with  portland  cement,  and  then  allowed 
to  set  for  about  10  days.  In  less  than  half  an  hour  after  starting  up, 
the  pounding  of  the  pebbles  caused  the  lining  to  break.  This 
'hasty  finish'  was,  at  the  time,  imputed  to  the  quality  of  the  cement 
used  and  to  the  fact  that  it  was  not  allowed  longer  to  set.  Mr. 
Drucker's  experience,  however,  shows  that  it  was  not  altogether 
due  to  such  causes.  We  next  tried  silex  lining;  but  while  this  did 
not  take  quite  as  long  to  place  and  for  its  cement  to  set,  as  did  the 
quartz  lining,  it  did  not  give  as  long  a  life  as  was  expected.  The 
silex  lining,  also,  acted  similarly  to  the  first  steel-plate  liners 
used,  giving  uneven  wear,  with  occasional  dropping  out  of  blocks. 

Then,  it  was  decided  to  try  wrought-iron  bars,  8  in.  wide  by 
1  in.  thick,  a  quantity  of  which  were  on  hand,  having  been  used 
as  connecting  straps  or  plates  at  the  joints  in  the  old  Cornish  pump 
in  the  Lent  shaft  of  the  same  company.  It  was  first  suggested  to 
bend  into  circles  to  fit  the  inner  surface  of  the  tube-mill  shell; 
but  as  we  had  no  machine-shop  rolls,  and  the  bending  would  have 
to  be  done  by  hand  in  the  blacksmith  shop,  that  idea  was  dropped. 
The  bars  were  cut  in  15  and  7 -it.  lengths  (15  ft.  being  the  longest 
that  could  be  handled  through  the  man-hole  of  the  tube-mill). 
These  were  put  in,  alternating  (so  as  to  break  joint),  lengthwise 
of  the  tube,  and  bolted  with  counter-sunk  bolts  that  passed  through 
the  shell.  The  nuts  and  washers  on  these  bolts  are  shown  by  the 
photograph.  The  bolt-holes  in  each  strap  are  'staggered ;'  and  it  was 
not  necessary  to  space  them  closely,  because  of  the  length  of  the 
pieces.  The  liners  were  all  drilled  to  the  same  measurements; 
and,  in  putting  in  the  first  set,  holes  were  drilled  in  the  tube-mill 
shell  to  correspond,  subsequent  sets  not  requiring  further  drilling 
of  the  shell. 

As  stated  above,  these  straps  or  bars  were  of  wrought  iron. 
They  give  a  life  of  between  three  and  four  months,  and  are  easy 
to  change — the  entire  operation  of  shoveling  the  load  of  pebbles, 
unbolting  old,  and  bolting  new  liners,  requiring  only  between  20 
and  24  hr.  The  width  of  the  straps,  8  in.,  does  not  allow  them  to 
fit  closely  to  the  curve  of  the  shell,  but  that  is  an  advantage, as  it 
has  a  tendency  to  turn  the  pebbles  over  on  themselves,  instead  of 


TUBE-MILL  LINING.  209 

sliding,  which  action  wears  out  the  liners  rapidly.  This  mill  has 
been  grinding  from  50  to  75  tons  daily.  The  portion  of  the  stamp- 
mill  product  requiring  re-grinding  is  principally  a  tough,  hard, 
chalcedonic  quartz. 

WALTER  W.  BRADLEY. 
Berkeley,  December  10. 


CYANIDE  CLEAN-UP 
BY  JAMES  E.  THOMAS 

1         (January  12,  1907) 

*In  designing  a  milling  plant  it  has  always  been  the  practice 
to  erect  a  separate  room  for  cleaning  and  pressing  amalgam, 
and  for  treating  any  rich  product,  such  as  die  sand,  etc.,  and  I  think 
it  is  still  more  important  that  a  separate  room  or  floor  should  be 
set  aside  for  the  corresponding  operations  in  a  cyanide  plant,  as 
the  liability  of  losses  occurring  in  handling  gold  slime  is  much 
greater  than  in  handling  amalgam. 

I  therefore  propose  bringing  forward  a  few  suggestions  with 
the  view  of  evoking  discussion  on  the  subject — too  long  neglected — 
so  that  the  engineers  who  design  these  plants  may  have  a  fairly 
definite  idea  of  what  is  really  required. 

The  clean-up  floor  should  have  a  drainage  separate  from  the 
rest  of  the  extractor-house  floor,  so  that  any  washings  shall  not 
be  contaminated  with  oil  and  grease  from  the  pumps,  etc.,  and  may 
be  run  into  a  sump  from  which  the  residue,  after  settlement, 
may  be  easily  collected  and  included  in  the  next  clean-up.  Means 
of  transport  of  the  gold-bearing  zinc,  etc.,  from  the  extractor- 
boxes  to  the  acid-tubs  should  be  somewhat  better  than  those 
afforded  by  the  proverbial  Kaffir  and  a  bath  or  bucket.  Much  time 
and  also  labor  is  wasted  by  that  method.  An  overhead  crawl 
with  tipping  buckets  could,  I  imagine,  be  easily  installed  in  most 
plants  and  would  soon  pay  for  itself  by  the  saving  of  time  and  labor, 
not  to  mention  the  decrease  in  liability  of  having  gold  slime  acci- 
dentally spilt  on  the  extractor-house  floor,  whence  it  is  apt  to  be 
carried  by  the  traffic  to  the  outside  of  the  building  and  lost. 

The  acid-treatment  plant  is  often  totally  inadequate  for  the 
proper  dissolving  of  the  zinc  and  insufficient  allowance  made  for 
the  washing  of  the  gold  slime  before  filter-pressing.  I  find  it  better 
to  have  two  acid-treatment  tubs  of  a  certain  capacity  than  to 
have  only  one  of  the  same  total  capacity,  as,  when  two  are  in  use, 
one  may  be  fed  while  the  other  is  suffering  from  a  threatened  at- 
tack of  'boiling  over,'  while,  when  only  one  is  installed,  nothing  can 
be  done  until  the  attack  has  succumbed  to  the  'cold  water  cure.' 

*Abstracted  from  The  Journal  of    the  Chemical,  Metallurgical  &  Mining  Society  of  South 
Africa,  October,  1906. 


CYANIDE  CLEAN-UP.  211 

A  stoppage  at  the  acid-tubs  throws  back  the  whole  clean-up,  and 
the  time  thus  lost  cannot  be  made  up. 

When  filter-pressing  is  begun  I  have  always  found  that  it 
may  be  much  more  quickly  accomplished  when  the  gold  slime  is 
drawn  from  the  bottom  of  the  washing  vat  than  when  the  suction 
from  the  filter-press  pump  is  slung  over  the  side  of  the  vat.  As  the 
gold  slime  is  very  heavy,  it  is  advisable  to  use  a  specially  short 
length  of  hose  for  the  filter-press  pump  suction.  If,  when  running 
down  the  charges  from  the  acid-treatment  tubs,  everything  is 
put  through  a  64-mesh  screen  and  the.  contents  of  the  washing  vat 
kept  in  agitation  while  the  press  is  being  filled,  there  is  no  danger 
of  the  hose  over  the  suction  drain-pipe  becoming  choked. 

The  use  of  filter  papers  over  the  cloths  of  the  press  is  also 
to  be  recommended,  as  filling  is  thereby  facilitated  and  the  life 
of  the  cloths  is  prolonged,  as  no  scrubbing  is  required  to  clean  them. 

The  filter-presses  supplied  have  invariably,  in  my  experience, 
the  openings  to  the  hollow  frames  left  rough  cored  and  with  a 
quantity  of  fused  molding  sand  blocking  the  passages.  By  having 
these  openings  filed  out  so  that  the  combined  area,  in  a  full  press, 
is  equal  to  or  greater  than  that  of  the  filling  channel  and  with  a 
slight,  increase  of  area  toward  the  inside  of  the  frames,  there  will 
be  less  liability  of  their  choking,  and  the  press  may  be  filled  in  about 
30%  less  time  than  when  they  are  left  rough. 

For  washing  the  cakes  while  in  the  press  it  is  advisable  to  use 
hot  water,  not  only  for  its  better  washing  effect,  but  also  because 
the  cakes  can  be  got  out  dry,  even  if  there  is  only  a  layer  of  gold 
slime  on  the  papers  or  cloths.  A  400-gal.  tank  placed  over  the  flue 
of  the  calcining  furnace,  if  the  latter  is  fairly  close  at  hand,  so  as 
to  utilize  the  heat  from  the  escaping  gases,  will  generally  be  found 
capable  of  giving  enough  hot  water. 

It  is  essential  that  a  vat  large  enough  to  take  all  the  washes 
from  the  washing  vat  and  the  filter-press  be  installed,  so  that 
the  Washes  may  receive  further  treatment  before  being  run  to 
waste. 

Gold  has  been  found  to  be  present  in  solution  in  the  acid 
washes.  This  is  apparently  due  to  the  presence  of  hydrocyanic 
acid.  The  more  completely  the  acid  treatment  is  carried  out, 
that  is,  when  no  zinc  is  left  undissolved,  the  more  danger  there  is 
of  gold  being  redissolved.  It  is  therefore  advisable  to  have  the 
washings  slightly  acid  and  then  sprinkle  zinc  fume  over  the  surface, 


212  RECENT  CYANIDE  PRACTICE. 

meanwhile  keeping  the  solution  agitated.  This  should  be  done 
each  time  a  charge  from  the  acid-tubs  is  transferred  for  washing. 
After  the  clean-up  is  over  it  is  advisable  to  have  the  contents 
of  the  large  vat  for  the  washings  assayed,  after  good  settlement, 
and,  if  necessary,  more  zinc  fume  can  be  added  before  the  solution 
is  run  to  waste.  By  this  means  the  gold  in  acid  washes  run  to  waste 
may  be  reduced  to  0.07  dwt.  per  ton,  whereas  the  ordinary  acid 
washes  will  probably  carry  1.5  dwt.,  or  more,  per  ton.  Copper 
sulphate,  finely  divided  iron,  and  charcoal  were  also  used  for  this 
purpose  in  the  laboratory  experiments,  but,  as  zinc  fume  gave  the 
most  satisfactory  results,  it  was  tried  on  a  working  scale  with 
such  success  that  it  has  been  used  on  all  the  mines  of  the  Consoli- 
dated Gold  Fields  group  ever  since  a  supply  could  be  procured.. 
It  is  prepared  by  the  distillation  of  zinc  in  vacua  and  should  be 
packed  in  air-tight  cases,  as  it  oxidizes  readily  on  exposure  to  the 
atmosphere  and  is  afterward,  of  course,  useless  for  this  purpose. 
From  five  to  seven  pounds  are  sufficient  to  treat  washes  amounting 
to  about  100  tons. 

For  taking  off  the  acid  washes  from  the  washing  vat  it  is 
advisable  to  use  a  decanter.  If  the  arm  of  the  decanter  be  painted 
white,  the  operator  can  see  at  a  glance  whether  the  solution  is 
clear  enough  to  draw  off  or  not.  The  paint  will  last  through 
a  clean-up  and  can  be  easily  renewed.  The  washing-vat  may 
have  a  false  bottom  of  cement  sloping  toward  the  outlet  to  enable 
it  to  be  more  easily  cleaned  out.  The  cement  should  be  painted 
over  with  P.  &  B.  acid-proof  paint  after  each  clean-up.  If  this  is 
done  it  will  show  no  signs  of  wear.  When  the  paint  is  being  applied 
it  is  as  well  to  keep  an  eye  on  the  person  doing  the  job,  as  I  have  had 
a  Kaffir  overcome  with  the  fumes  from  the  paint  when  at  work 
on  the  bottom  of  a  vat  10  ft.  deep.  He  quickly  recovered  on 
being  taken  to  the  fresh  air. 

Stirring  gear  for  the  acid-dissolving  tubs  should  be  installed, 
but  the  motion  should  be  reversible,  as  it  is  often  found  expedient 
to  reverse  the  direction  of  stirring  in  order  to  help  the  dissolving 
of  the  zinc  and  to  free  any  which  may  have  collected  round 
the  upright  carrying  the  paddles. 


THE  MOORE  AND  BUTTERS  FILTERS 

(January  12,  1907) 

The  Editor: 

Sir — The  article  by  Mr.  Nutter  on  the  Moore  filter  in  your 
issue  of  December  15  is  both  interesting  and  instructive.  There 
are,  however,  several  serious  errors  in  it  which  do  an  injustice 
to  the  Butters  filter,  and  which  should  be  corrected  immediately. 
In  discussing  a  plant  to  treat  350  tons  of  slime,  as  described  by  Mr. 
Nutter,  a  comparison  with  the  plant  erected  (at  Millers,  in  Nevada) 
for  the  Tonopah  company,  will  be  in  order.  This  Butters  slime- 
filter  consists  of  216  leaves,  and  would  handle  about  300  tons 
of  the  Liberty  Bell  slime,  and  250  leaves  would  easily  handle 
the  mill  output  of  350  tons  per  day.  Such  a  plant  would  require 
instead  of  eight  7-in.  pumps  as  estimated  by  Mr.  Nutter,  only 
one  pump  that  would  transfer  the  pulp  or  water  in  10  minutes. 
It  is  very  difficult  to  calculate  centrifugal  pump  capacities  working 
on  a  material  of  such  variable  consistence  as  slime,  but  judging  from 
previous  experience  with  different  slimes  a  9-in.  pump  would 
be  amply  large;  and  as  48-in.  pumps  are  regularly  used  to  transfer 
sand  in  dredging,  it  is  hardly  in  order  to  call  a  9-in.  pump  "large," 
or  to  consider  it  or  its  valves  difficult  of  operation. 

The  light  crane  mentioned  by  Mr.  Nutter  would  not  be  neces- 
sary, as  a  half-ton  chain-block,  with  crawl,  would  handle  the 
Butters  leaves  when  such  handling  became  necessary,  which, 
by  the  way,  would  be  rare. 

As  regards  the  quantity  of  slime  to  be  pumped,  it  is  certainly 
not  fair  to  require  the  handling  of  the  large  quantity  needed  to 
fill  Mr.  Nutter's  filter- vats,  which  are  not  designed  as  is  the  Butters 
filter-box,  to  contain  barely  enough  slime  to  cover  the  leaves. 
Neither  is  it  a  fair  proposition  to  require  that  the  slime  be  pumped 
against  the  maximum  head  of  19  ft.,  when  a  properly  designed 
plant,  even  when  built  on  level  ground,  has  a  maximum  lift  of 
10  ft.  and  a  minimum  of  0  ft.  In  other  words,  one  properly 
designed  box  for  250  Butters  leaves  will  contain  approximately 
7,000  cu.  ft.  instead  of  the  24,000  cu.  ft.  capacity  of  the  eight 
filter-vats  that  Mr.  Nutter  considers  necessary.  The  use  of  such  a 
box  would  make  available  for  water  and  slime  storage  the  vats 


214 


RECENT  CYANIDE  PRACTICE. 


now  used  for  filtering  and  washing,  thus  obviating  the  necessity 
of  installing  the  two  storage  tanks  he  mentions.  «••«<  p*-'w*&-*  *••••  t  j 
Instead  of  the  time  items  being  as  given  by  Mr.  Nutter  in  the 
cycle  of  operations,  the  following  in  the  opinion  of  the  writer, 
would  more  nearly  approximate  actual  running  conditions: 


Operations. 

Moore. 

Butters. 

Butters 
gravity. 

Loading          

1  hr. 

1  hr. 

1  hr. 

Transferring  (filters)  
Milling  with  water                .  .  . 

10  min.  (pulp) 
Nil 

10  min. 
10  " 

2  min. 
5  " 

Washing 

1  hr. 

1  hr. 

1  hr. 

Discharging 

10  min 

10  min. 

10  min. 

Transferring  (niters)  

10  '!         (pulp) 

10  " 

2  " 

Total  

2  hr.  30  min. 

2  hr.  40  min. 

2  hr.  19  min. 

Without  knowing  the  conditions  as  they  exist  at  the  Liberty 
Bell  that  would  influence  the  cost  of  a  filter  installation,  such 
as  present  arrangement  of  vats  and  tanks,  power  required  by 
the  Moore  filter,  ground  contours,  etc.,  I  am  unable  to  carry  this 
comparison  to  its  logical  conclusion,  wherefore  it  is  incomplete. 

A  statement  from  Mr.  Nutter  as  to  why  it  would  not  be  better 
to  install  a  properly  designed  filter-box;  why  a  gravity  plant 
could  not  be  placed;  and  why  one  9-in.  pump  would  not  be  suffi- 
cient, would  seem  to  be  in  order. 

MARK  R.  LAMB. 

Mexico  City,  December  22. 


A  SIPHON  DEVICE  FOR  REMOVING  FLOATING 

MATERIAL 
BY  EDWARD  S..WIARD 

(February  2,   1907) 

The  device  described  and  illustrated  in  this  article  was  used 
by  the  writer  in  a  mill  in  northern  Idaho  to  remove  particles  of 
floating  galena  from  the  surface  of  the  water  in  a  long  V-shaped 
tank,  distributing  thickened  pulp  to  a  number  of  Wilfley  tables 
and  vanners.  Owing  to  the  manner  of  mining,  the  milling  ore 
contained  an  extraordinary  amount  of  wood,  causing  more  than 
the  usual  trouble  of  stopping  up  plugs  and  clogging  the  riffles 
of  the  Wilfley  tables.  An  examination  of  the  floating  material 
showed  it  to  consist  largely  of  fine  bits  of  wood  to  which  had  adhered 
scaly  pieces  of  galena;  the  adhesion  of  the  two  being  possibly 
assisted  by  a  film  of  grease  on  the  wood.  The  galena  was  rather 
richer  in  silver  than  the  regular  run  of  concentrate ;  tests  with  sil- 
ver-leaching salts  and  an  examination  with  the  microscope  show- 
ing the  increase  over  the  normal  proportion  to  be  due  to  tetrahe- 
drite.  This  mineral  was  in  minor  amount  in  the  ore  as  it  came 
to  the  mill,  the  predominant  silver  mineral  being  argentite.  A 
little  galena  was  lost  by  greasy  flotation.  The  undressed  ore 
contained  large  amounts  of  spathic  iron  and  the  tank- water  was 
slightly  acid.  Apparently,  the  top  layers  of  the  water  in  the  tank 
were  perfectly  clear  but  the  insertion  of  a  baffle-board  would  cause 
a  black  scum  to  dam  up  behind  it,  constantly  being  augmented, 
and  spreading  over  the  surface  of  the  water.  The  galena  could 
readily  be  separated  from  the  wood  by  agitation;  after  shaking  a 
portion  of  water  and  scum  in  a  beaker,  the  wood  would  rise  to  the 
top  and  the  galena  settle  to  the  bottom. 

The  water  from  the  siphon  was  used  to  wash  down  the  con- 
centrate formed  by  the  vanners.  Clean  water  was  scarce  and, 
it  being  necessary  to  make  a  concentrate  high  in  lead,  it  was  not 
possible  to  use  the  overflow  water  of  the  tank  for  sluicing  purposes. 
The  overflow  of  the  tank  contained  a  noteworthy  quantity  of  fine 
matter,  which  was  further  settled  on  the  lower  floor. 

The  device,  herewith  illustrated,  is  suggestive  of  a  means  of 


216  RECENT  CYANIDE  PRACTICE. 

reducing  the  volume  of  water  flowing  through  a  tank.  The  slime 
and  sand  treated  in  the  mill  under  discussion  were  rather  free  from 
clayey  matter  and  the  surface  water  but  a  few  feet  from  the  feed 
end  of  the  tank  was  very  nearly  clear.  The  device  floated  in  the 
water  about  two-thirds  the  way  from  the  feed  end  to  the  over- 
flow end,  but  it  would  have  been  possible  to  have  placed  it  much 
closer  to  the  feed  end  of  the  tank  and  obtain  water  free  from  low- 
grade  slime.  For  the  purpose  of  merely  removing  comparatively 
clean  water,  a  number  of  the  devices  could  have  been  used. 

The  two  float-tanks  should  properly  be  made  of  thin  sheet 
aluminium.  My  floats  were  made  of  No.  30  sheet  iron  heavily 
coated  with  bitumen.  At  the  top  the  sides  are  bent  over  a  heavy 
wire,  bent  to  the  shape  of  the  tank,  to  give  stiffness.  The  rubber 
tubing  used  was  J  in.  outside  diameter,  with  walls  3/32  in.  thick. 
The  tubing  should  be  thin-walled,  so  as  not  to  interfere  with  the 
free  vertical  movements  of  the  floats.  The  bracket  between 
the  floats,  supporting  the  tank-end  of  the  tubes  and  the  inverted 
mushrooms,  is  made  of  light  strips  of  wood  stiffened  by  four  little 
angle -irons  in  the  corners.  These  can  be  quickly  made  and  bored 
and  countersunk  for  wood  screws  by  the  mill-blacksmith.  Care 
should  be  taken  to  make  the  upper  row  of  holes  in  the  bracket 
vertically  above  the  corresponding  lower  ones.  These  holes 
should  be  of  a  little  less  diameter  than  the  tubing;  the  tubing  will 
then  be  firmly  held  and  yet  adjustable.  The  inverted  mushrooms 
or  strainers  are  made  of  No.  24  copper  plate.  With  the  form  of 
strainer  used,  the  pull  due  to  the  siphon  action  drew  the  top  layer 
of  water  downward  and  in  from  the  sides  firmly  and  gently.  With 
a  simple  tube  in  the  water  a  current  would  be  created  from  the  bot- 
tom of  the  tank  that  would  stir  up  the  low-grade  slime  below  the 
upper  layers  of  water.  The  nipples  on  the  IJ-in.  pipe  are  short 
pieces  of  pipe  screwed  into  the  sides.  The  tanks  are  prevented 
from  moving  from  their  positions  by  strings  fastened  from  their 
points  to  the  nipple  pipe ;  they  are  not  shown  in  the  drawing.  The 
little  strips  of  wood  from  the  points  of  the  floats  to  the  sides  of 
the  tank  are  in  the  nature  of  baffles  to  cause  the  floating  material 
to  converge  toward  the  mushrooms  and  prevent  its  passage 
between  the  floats  and  the  sides  of  the  tank.  A  similar  strip 
floats  behind  the  mushrooms  to  prevent  floating  material  from 
passing  by  them. 


DEVICE  FOR  REMOVING  FLO  A  TING  MA  TERIAL.    217 


DETAIL.  O 


T\ 


7JT7 


PL  A>N    

S;»l«    6w!3  •  lit 


SIPHON     DELV/ICE: 

fr 
REMOVING  SLIME. 


Fig.  25. 

The  siphon  device  is  started  by  opening  the  valve  from  the 
high-pressure  supply;  after  it  is  started,  the  valve  is  closed  and 
regulation  is  effected  by  the  valve  A.  To  avoid  a  climb  to  the  tank, 
a  second  valve  (B)  was  placed  on  the  vanner  floor  for  starting  or 
stopping  the  siphon. 


THE  BUTTERS  FILTER 
BY  MARK  R.  LAMB 

(February  2,  1907) 

The  accompanying  illustration  shows  a  Butters  filter  with  the 
necessary  tanks  and  pumps.  The  filter  is  extremely  simple  and 
consists  merely  of  two  sheets  of  canvas  sewn  to  a  core  of  cocoa- 
matting.  These  resultant  leaves  or  cells  are  supported  by  a  wooden 
strip  at  the  top  and  by  a  frame  of  half-inch  pipe  at  the  sides  and 
bottom.  The  cells  are  connected  by  short  nipples  and  hose  to  the 
vacuum-drum.  When  the  filter-box  is  filled  with  pulp,  which  has 
been  previously  agitated  with  solution,  the  vacuum  draws  the 
solution  from  the  slime,  leaving  the  latter  on  the  leaves  in  the  form 
of  a  layer.  This  layer  is  made  from  0.75  to  1.5  in.  thick,  depending 
on  the  class  of  slime.  During  the  time  the  slime-cake  is  being  formed 
the  filter-box  is  kept  full  of  pulp,  the  additions  replacing  the  solu- 
tion withdrawn  through  the  cells  and  keeping  the  slime  agitated. 

The  layer  forms  continuously  and,  as  would  be  expected  from 
the  nature  of  the  operation,  its  thickness  varies  from  top  to  bottom, 
depending  upon  the  permeability  of  the  stuff  deposited.  In  other 
words,  the  slime  resulting  from  all-sliming,  which  contains  fine 
sand,  forms  a  thicker  layer  on  the  lower  portion  of  the  leaf  than  on 
the  upper.  This  thicker  part  is  more  permeable  and  is  washed  in 
exactly  the  same  time  as  the  thinner  but  denser  upper  part. 

After  the  layer  of  slime  has  attained  the  desired  thickness, 
the  pulp  remaining  in  the  box  is  drawn  off  to  the  pulp-sump, 
and  the  box  is  filled  with  water.  This  water  is  drawn  through 
the  slime  until  the  latter  is  thoroughly  freed  from  solution  and  metal 
in  solution.  The  vacuum  is  then  broken  and  clear  water  intro- 
duced under  slight  pressure  into  the  interior  of  the  leaves.  This 
dislodges  the  slime  which  is  discharged  from  the  hopper  bottom 
through  a  gate- valve.  Where  it  is  desirable,  a  large  portion  of  the 
water  remaining  in*  the  box  can  be  withdrawn  before  the  slime  is 
discharged,  and  if  water  is  very  expensive  the  slime  can  be  dislodged 
with  compressed  air  and  trammed  from  the  filter-box.  The  small 
centrifugal  pump  returns  the  pregnant  solution  to  zinc  or  fume  or 


THE  BUTTERS  FILTER. 


219 


electrolytic  precipitation  boxes.  The  large  centrifugal  pump 
returns  the  excess  of  unfiltered  slime  to  its  storage  vat.  All 
valve-stems  are  extended  to  the  operating  floor,  which  permits 
one  man  to  treat  almost  any  tonnage.  The  canvas  does  not  seem 
to  deteriorate,  one  set  having  been  in  service  over  two  years.  The 
lime  used  in  neutralizing  acidity  appears  to  protect  the  fibre. 


Fig.  26.     Butters  Filter. 


When  this  calcium  carbonate  accumulates  sufficiently  to  delay 
operations,  it  is  removed  by  subjecting  the  leaves  to  a  bath  of 
2%  HC1. 

The  filter-box  may  be  made  either  of  wood  or  iron,  as  may 
seem  advisable,  depending  on  the  locality,  costs,  and  freight. 
Where  the  site  does  not  permit  of  filling  and  emptying  the  box 


220  RECENT  CYANIDE  PRACTICE. 

by  gravity,  the  pulp  is  circulated  and  transferred  by  the  pump. 
The  valves  in  such  a  system  are  all  placed  near  the  pump  and  con- 
trolled from  the  operating  platform  above  mentioned.  The  wash 
attained  by  the  filter  is  notably  perfect  and  is  accomplished  by 
the  use  of  a  minimum  of  water. 

Slime  is  now  being  treated,  resulting  from  the  milling  of 
Tonopah  ore,  which  it  would  not  be  possible  to  treat  by  decantation, 
and  for  which  a  filter-press  installation  would  be  prohibitively 
expensive,  as  well  in  first  cost  as  in  labor  and  power.  This  filter 
combines  the  best  features  of  the  Moore,  Butters,  and  Cassel 
patents  and  will  be  the  means  of  extracting  precious  metal  from 
slime  not  amenable  to  treatment  by  any  other  method,  as  well 
as  from  sand  now  treated  by  percolation,  but  which  will  be  ground 
much  finer  and  treated  by  agitation  and  filtration. 


THE  RIDGWAY  FILTER 

(February  9,  1907) 

*This  invention  is  designed  particularly  for  treating  slime 
containing  gold  in  solution.  A  trial  machine  was  built  on  the  Great 
Boulder  mine,  at  Kalgoorlie,  and  has  been  constantly  in  operation 
since  January,  1906. 

This  machine  consists  of  12  flat  cast-iron  filtering  frames 
(T),  which  are  in  the  form  of  sectors  of  a  circle.  The  frames  are 
corrugated  on  their  under  surfaces,  and  to  these  corrugated  sur- 
faces screens  are  attached;  ordinary  filter-cloth  is  fixed  over  the 
screens.  The  frames  are  suspended  horizontally  from  radially 
arranged  levers  (X) ,  the  inner  ends  of  which  are  connected  to  a  ver- 
tical centre  column  or  spindle,  provided  with  internal  compartments. 
Each  filtering  frame  is  also  connected  by  three  radial  pipes  and  rub- 
ber hoses  to  different  compartments  in  the  central  column. 

The  outer  edges  of  the  filtering  frames  form  the  periphery 
of  a  circle  12  ft.  in  diameter;  immediately  outside  this  periphery 
is  placed  a  circular  rail  track  (Z) ,  and  to  the  outer  end  of  the  levers 
(X)  are  attached  wheels  or  rollers  (T1),  of  4  in.  diam.  The  wheels 
support  the  levers  and  run  on  the  circular  track  (Z),  which  is  car- 
ried on  the  outer  edge  of  an  annular  trough  under  the  filtering 
frames.  The  trough  is  divided  into  three  compartments — one 
for  slime-pulp,  one  for  wash-solution,  and  one  (without  a  bottom) 
for  residue  discharge.  The  general  level  of  the  track  (Z)  is  such 
that  the  frame  has  its  lower  surface  only  immersed;  the  track, 
however,  has  elevated  portions  so  arranged  that  when  the  cen- 
tral columns  and  frames  are  rotated,  the  wheels,  in  running  up 
the  elevation,  lift  the  filtering-frames  out  of  one  compartment, 
and,  on  descending,  lower  the  frame  into  another. 

The  lower  part  of  the  central  column  has  two  passages,  into 
which  the  solutions  are  drawn,  by  a  vacuum,  through  the  radial 
pipes  that  connect  with  the  filtering  frames — the  vacuum  being 
produced  by  a  pump  connected  with  the  openings  (G1  and  L) 
near  the  bottom  of  the  column — air-tight  connections  between 
rotating  and  stationary  parts  being  secured  by  means  of  glands 
and  stuffing-boxes. 


*From  the  Monthly  Journal  of  the  Chamber  of  Mines  of  Western  Australia.     November,  1906. 


K. 

1    1 

1C 

31 

, 

L_l 

* 

\ 

^— 

c1        i 

^% 

s 

• 

Fig.  27.     The  Ridgway  Filter. 


THE  RIDGWAY  FILTER.  223 

A  nest  of  three  valves  (U)  is  placed  in  the  pipes  between 
the  column  and  each  filter-frame ;  each  of  the  three  valves  is  auto- 
matically operated  while  the  machine  is  in  motion  by  small  roll- 
ers (V)  passing  over  elevations  on  one  or  other  of  the  three  tracks 
shown  at  (W) ;  the  gold  solution  is  thus  delivered  into  one  compart- 
ment of  the  central  column  through  one  of  the  valves,  and  the 
wash  solution  into  the  other  compartment  through  another  valve, 
thus  providing  for  the  two  solutions  being  kept  separate.  A  third 
pipe  connects  the  third  valve  (at  U)  with  the  top  or  compressed 
air  section  of  the  column  (at  B),  and  while  the  frame  is  passing 
over  the  discharge  chute  this  valve  is  automatically  opened  by 
its  roller  and  a  puff  of  compressed  air  enters  the  filter-frame  and 
displaces  the  residue  adhering  to  the  cloth ;  the  residue  falls  through 
the  discharge  chute  ( D1 )  into  a  dump-truck.  Each  frame  acts 
independently,  having  its  own  roller,  set  of  valves,  and  connections 
with  the  central  column;  and  each  frame  and  its  adjuncts  form  a 
complete  self-acting  unit.  The  accompanying  drawing  shows  a 
single-plunger  air-compressor  (at  C),  self-contained  and  driven 
by  the  machine  itself;  the  compressed  air  can,  in  many  instances, 
be  supplied  conveniently  from  other  sources. 

The  machine  requires  about  J  h.p.,  and  is  driven  (in  the 
direction  of  the  hands  of  a  watch)  with  a  6-in.  belt  on  a  42-in. 
pulley  keyed  to  the  top  of  the  central  column  (at  5) ,  and  makes  one 
revolution  per  minute.  The  vacuum  is  on  the  filter-plate  the  whole 
time  it  is  immersed — whether  in  the  pulp  or  in  the  solution  wash. 
Each  filter-frame  is  13  seconds  in  the  pulp  (from  B1  to  B1), 
seven  seconds  on  the  elevated  portion  while  passing  from  the  slime 
to  the  wash  compartment,  30  seconds  passing  through  the  wash 
(C1  to  C1),  seven  seconds  lifting  and  drying,  and  three  seconds 
blowing  residue  off  (at  D1).  During  the  period  in  which  the 
frame  is  passing  from  the  pulp  to  the  wash,  the  vacuum  is  on  for 
•one  second  only  while  the  frame  is  rising,  and  one  second  only 
while  it  is  descending  into  the  wash,  thus  giving  the  pulp  adhering 
to  the  underside  of  the  frame  an  air-leaching  of  two  seconds' 
duration.  This  period  of  leaching  may  be  varied  to  suit  the  par- 
ticular nature  of  the  slime  under  treatment  or  the  thickness  to 
which  it  has  formed  on  the  cloth,  which  is  usually  about  f  of  an 
inch.  The  supply  of  pulp,  wash-solution,  or  water  into  the  annular 
troughs,  (51  and  C1),  is  regulated  by  means  of  float-valves  in 
the  receiving  compartments  (G1  and  Gl) ;  the  pulp  is  kept  from 


224  RECENT  CYANIDE  PRACTICE. 

settling  by  the  revolution  of  small  agitators  driven  by  a  rope 
passing  round  pulleys  attached  to  their  spindles,  which  project 
through  glands  and  stuffing-boxes  in  the  bottom  of  the  receiver 
(at  El  and  E1),  etc.  By  means  of  the  float-valve  in  the  pulp- 
receiver  (Gl  ),  the  pulp  supply  is  taken  automatically  from  the 
pipes  through  which  the  Dehne  presses  are  charged;  thus,  in  order 
to  compare  the  efficiency  of  extraction  by  the  machine  with  that 
of  the  presses,  a  portion  of  the  general  pulp  is  taken  as  each  Dehne 
press  is  filled. 

From  0.8  to  one  ton  of  wash  is  used  per  ton  of  dry  slime, 
and  the  residues  contain  from  28  to  33%  moisture,  and  from  nil 
to  a  trace  of  KCN  and  soluble  gold.  The  tonnage  treated  in  24 
hours  and  percentage  of  moisture  contained  in  the  residues  vary 
according  to  the  variations  in  the  pulp.  With  clean  quartz 
slime  of  a  consistence  of  from  42  to  44%  solid,  and  a  fineness  of 
about  92%  through  a  screen  having  200  holes  per  linear  inch, 
and  a  vacuum  of  20  in.,  this  machine  will  treat  50  tons  of  dry 
slime  per  24  hours,  leaving  a  residual  moisture  of  30  per  cent. 

On  a  clay  slime  the  output  will  decrease  to  25  tons  per  24 
hours,  and  the  residual  moisture  will  increase  35%,.  A  trial  was 
made  on  the  old  battery  slime;  the  original  assay  value  was  7  dwt., 
the  gold  in  residue  18  gr.,  moisture  in  residue  35%,  soluble  gold  in 
residue  nil;  this  was  treated  at  the  rate  of  25  tons  per  24  hours. 

Each  frame  has  four  square  feet  of  filtering  area  and  about 
0.8  square  yard  of  cloth  is  used  to  cover  each  frame.  The  life  of 
a  cloth  on  slime  from  the  Great  Boulder  roasted  ore  is  about  14 
days,  or  700  tons  of  slime  for  9.6  sq.  yd.  of  cloth. 

The  vacuum  pump  has  a  piston  sweep  of  80  cu.  ft.  per  min., 
and,  with  a  20-in.  vacuum,  requires  3J  h.p.  The  machine  itself, 
without  the  self-acting  air-compressor,  requires  about  ^  h.p.,  and 
allowing  1  h.p.  for  the  agitators  in  the  pulp-trough  and  pulp- 
receiver,  and  for  friction  in  the  counter-shaft,  a  total  of  5  h.p. 
is  required  to  drive  the  equipment  described. 

As  the  machine  is  absolutely  automatic  in  its  entire  opera- 
tion, no  additional  labor  is  employed  in  running  it.  Taking  into 
consideration  that  this  is  the  first  machine  made  of  this  pattern,  the 
repairs  and  renewals  have  not  been  abnormal. 


THE  RIDGWAY  FILTER.  225 

The  working  costs  during  the  last  three  months  have  been: 

Pence. 

Filter-cloth 0.3  per  ton 

Horse-power 2.4     " 

Repairs  and  renewals 1.0     " 

Total 3.7     " 

It  has  been  impossible  to  segregate  the  labor  cost  on  this 
machine  (other  than  those  included  in  repairs  and  renewals), 
as  during  the  whole  run  any  slight  attention  necessary,  other 
than  greasing,  has  been  performed  by  the  shift-boss  on  duty. 

The  method  of  operating  the  machine  is  as  follows:  The 
agitators  in  the  pulp  compartment  of  the  annular  trough  are  first 
set  in  motion,  being  driven  independently  of  the  machine;  the 
pulp-compartment  is  filled  to  normal  level  with  agitated  pulp, 
and  the  wash-compartment  with  wash-solution.  The  vacuum 
pump  is  started,  and  the  machine  is  set  in  motion  by  applying 
a  tension  pulley  to  the  belt  on  the  pulley  attached  to  the  top  of 
the  centre  column  of  the  machine,  thus  rotating  the  centre  column, 
which  imparts  the  motion  to  the  filter-frames  by  the  pipes  and 
levers,  causing  the  rollers  (  T1  )  supporting  the  outer  end  of  the 
levers  from  which  the  filter-frames  are  suspended,  to  travel  on 
their  track  (Z) .  As  the  action  of  all  the  frames  and  their  connec- 
tions is  similar,  one  only  need  be  described.  Assuming  that  a 
frame  has  just  passed  over  the  discharge  chute  and  is  on  the  ele- 
vated portion  of  the  track,  it  then  descends  an  incline  on  the 
track  to  the  normal  level,  and  the  cloth  on  the  underside  of  the 
frame  is  immersed  in  the  pulp ;  at  the  same  time,  the  gold  solution 
valve  (at  U)  is  opened  by  a  roller  (at  V)  running  up  an  incline 
on  its  track  (W),  and  similarly  to  the  action  of  the  elevating 
rollers  (at  T1)  on  the  track  (at  Z),  thus  opening  direct  connection 
between  the  filter-frame  and  the  vacuum  which  is  maintained 
in  the  centre  column;  the  vacuum  draws  the  liquid  through  the 
cloth  and  leaves  the  solids  adhering  to  it.  The  roller  (T1  )  on 
the  outer  end  of  the  lever,  while  continuing  on  the  level  track, 
keeps  the  cloth  submerged  till  another  incline  is  reached,  up  which 
it  then  ascends,  lifting  the  frame  out  of  the  pulp-trough;  on  de- 
scending the  incline  again  to  normal  level,  the  frame  is  lowered 
into  the  wash-solution.  When  the  frame  ascended  from  the  pulp, 
the  gold-solution  valve  closed,  and  as  it  descended  into  the  wash  so- 
lution the  wash- valve  opened,  causing  the  vacuum  to  draw  the  wash 


226  RECENT  CYANIDE  PRACTICE. 

through  the  adhering  pulp,  which  is  usually  about  three-eighths 
of  an  inch  thick.  The  frame  continues  in  the  wash-trough  during 
the  travel  of  half  the  circle,  and  is  then  raised  by  similar  means 
to  those  already  described,  but  the  wash-valve  is  not  closed  till 
the  discharge  chute  is  reached,  thus  allowing  the  vacuum  to  remove, 
by  air-drying,  some  of  the  moisture  from  the  cake  of  slime  formed 
on  the  underside  of  the  cloth.  When  the  discharge  chute  is  reached, 
the  wash- valve  closes,  and  the  air-valve  in  connection  with  the 
upper  portion  (B)  of  central  column  is  opened,  admitting  a  puff 
of  compressed  air,  which  dislodges  the  cake  from  the  cloth  and 
precipitates  it  into  the  discharge  chute  (D1),  under  which  a  dump 
truck  is  placed  to  receive  residues.  The  compressed  air  required 
at  the  time  of  the  discharge  can  be  supplied  in  any  usual  way  or 
by  the  self-contained  arrangement  shown  in  the  drawing  at  C '.. 


THE  BUTTERS  FILTER 

(February  16,  1907) 

The  Editor: 

Sir: — In  a  recent  number  of  the  PRESS*,  Mr.  Mark  R.  Lamb, 
of  the  Butters  Co.,  has  criticised  a  comparison  I  madef  of  the  Moore 
and  Butters  niters  as  applied  to  conditions  at  the  Liberty  Bell  mill. 
Mr.  Lamb  claims  that  my  comparison  was  unjust  and  unfair 
to  the  Butters  process,  and  goes  on  to  say  that  instead  of  the  one  I 
made,  a  comparison 'with  the  Butters  installation  for  the  Tonopah 
Mining  Co.  at  Millers,  Nevada,  would  be  in  order. 

Since  reading  Mr.  Lamb's  article  I  have  obtained  additional 
information  covering  the  points  raised,  and  in  the  light  of  that  infor- 
mation I  am  forced  to  doubt  Mr.  Lamb's  data  and  question  his  con- 
clusions. Mr.  Lamb  does  not  state  specifically  that  all  of  his  data 
are  from  the  plant  at  Millers,  but,  as  that  plant  is  one  of  the  latest 
of  the  Butters  installations,  it  presumably  represents  the  best 
Butters  practice,  and  it  would  seem  fair  to  examine  Mr.  Lamb's 
statements  and  conclusions  in  the  light  of  facts  pertaining  to  that 
plant. 

Mr.  R.  Chester  Turner,  superintendent  for  the  Tonopah 
company,  and  Mr.  A.  R.  Parsons,  mill  superintendent,  have 
kindly  furnished  me  information  about  the  Millers  plant,  which  is 
given  below  in  parallel  column  with  Mr.  Lamb's  statements: 

Lamb.  Turner  &  Parsons. 

Capacity  of  filtering  vats Not  given  9,130  cu.  ft. 

Size  of  filters 5  by  10  ft.  J  4  ft.  9  in.  by  9  ft.  9  in. 

Number  of  filters 216  192 

Time  required  to  transfer  pulp 10  minutes  20  minutes 

Time  required  to  fill  vats  with  water      10  20 

Discharging  cake 10       "  Not  given 

Running  back  water Not  given  20 

Running  in  pulp 10  minutes  20 

Maximum  height  of  lift  during  trans- 
fer of  pulp  and  water,  by  centrif- 
ugal pumps 10  feet  25  feet 

It  would  have  seemed  in  order  for  Mr.  Lamb  to  have  made 
sure  of  his  own  ground  before  attacking  the  statements  I  made. 

*MINING  AND  SCIENTIFIC  PRESS,  January  12,  1907,  page  54. 
tMiNiNG  AND  SCIENTIFIC  PRESS,  December  15,  1906,  page  714. 
JGiven  in  personal  letter  to  me. 


228  RECENT  CYANIDE  PRACTICE. 

In  a  personal  letter  he  admits  the  fairness  of  my  assumption, 
that,  with  the  same  slime,  the  loading  and  washing  periods  and 
the  vacuum  required,  etc.,  can  be  figured  the  same  for  both  pro- 
cesses. Let  it  be  assumed  then  that  Liberty  Bell  slime  is  to  be 
handled  by  a  plant  built  of  the  same  units  as  at  Millers.  The 
treatment  cycle  would  be  as  follows : 

Loading 60  minutes 

Running  out  pulp   20 

Running  in  water 20 

Washing  cake , 60 

Discharging 15 

Running  out  water 20 

Running  in  pulp ' 20 


Total 215  minutes 

Total  time  of  cycle   3  hr.  35  min. 

Total  number  of  cycles 6.7  per  24  hr. 

Mr.  Lamb  states  that  250  leaves  or  niters  like  the  ones  in- 
stalled at  Millers  "would  easily  handle  the  mill  output  (Liberty 
Bell)  of  350  tons  per  day."  As  stated  in  my  previous  article 
45  changes  of  the  Moore  baskets  are  now  necessary  to  handle 
that  tonnage.  Each  basket  has  66  filters  six  by  eight  feet,  giving 
a  filtering  area  of  6,336  sq.  ft.  per  basket.  With  45  charges, 
then,  we  would  have  285,000  sq.  ft.  of  cake  formed.  The  6.7 
cycles  of  the  Butters  unit,  under1  consideration,  would  represent 
59,563  sq.  ft.  of  cake  formed,  as  the  96  filters  have  an  area  of 
8,890  sq.  ft.  To  handle,  then,  the  Liberty  Bell  tonnage  would 
require  4.79  vats  of  the  size  at  Millers,  or  460  leaves  instead  of 
the  250  that  Mr.  Lamb  gives  as  a  sufficient  number,  or  the  330 
Moore  leaves  now  doing  the  work. 

Again  Mr.  Lamb  states  that  one  properly  designed  box  for 
250  Butters  leaves  will  contain  approximately  7,000  cu.  ft.  If 
this  is  so,  why  were  not  the  Millers  boxes  properly  designed?  The 
two  contain  only  192  leaves  and  have  a  capacity  of  9,130  cu.  ft. 
These  two  boxes  have  an  aggregate  filtering  surface  of  17,780  sq. 
ft.,  which  gives  0.51  cu.  ft.  of  box  per  square  foot  of  filter.  The 
Moore  boxes  at  the  Liberty  Bell  have  a  capacity  of  3,050  cu.  ft. 
each,  as  stated  in  a  previous  article,  and  one  basket  has  6,336 
sq.  ft.  of  filter  surface.  This  gives  0.48  cu.  ft.  of  box  per  square 
foot  of  filter.  It  would  seem  from  this  that  the  Moore  boxes 
at  the  Liberty  Bell  are  rather  better  designed  for  Butters  process 
work  than  are  the  boxes  installed  by  Butters;  and  Mr.  Lamb's 


THE  BUTTERS  FILTER.  229 

contention  that  "it  is  certainly  not  fair  to  require  the  handling 
of  the  large, quantity  (of  slime)  needed  to  fill  (the  Liberty  Bell) 
filter  vats,  which  are  not  designed  as  in  the  Butters  filter-box, 
to  contain  barely  enough  slime  to  cover  the  leaves,"  rather 
falls  to  the  ground.  These  boxes  are  of  the  same  general  design, 
that  is,  they  are  rectangular  boxes  with  hopper-bottoms,  having 
a  60°  slope. 

Mr.  Lamb  advocates  the  use  of  one  large  filter-box  for  the 
Liberty  Bell,  instead  of  the  units  at  present  in  use  for  the  Moore 
process,  and  says  that  one  9-in.  pump  would  probably  handle 
the  pulp  in  10  minutes.  For  a  box  containing  250  Butters  leaves, 
the  capacity  would  be  11,800  cu.  ft.,  if  it  were  of  the  same  design 
as  the  boxes  at  Millers,  instead  of  the  7,000  cu.  ft.  'given  by  Mr. 
Lamb.  The  amount  of  pulp  and  water  to  move  would  be  about 
1,900  cu.  ft.  less  on  account  of  the  displacement  of  the  loaded 
filters,  giving  9,900  cu.  ft.  of  material  to  handle.  If  we  accept 
the  statements  of  pump  manufacturers — and  the  capacities  of 
their  pumps  aie  probably  not  under-estimated — a  15-in.  discharge 
pump  would  be  necessary  to  move  this  volume  of  material  in 
ten  minutes,  or  a  12-in.  pump  in  20  minutes.  If  we  put  our 
460  leaves  in  one  box,  a  15-in.  pump  would  be  necessary  for  moving 
the  pulp  in  20  min.,  and  a  20-in.  pump  necessary  to  do  it  in  10 
minutes. 

His  proposition  to  use  a  single  large  vat  also  involves  the 
condition  of  maximum  power  consumption  where  power  is  bought 
on  peak  load. 

Mr.  Lamb's  statement  that  "as  48-in.  pumps  are  regularly 
used  to  transfer  sand  in  dredging,  it  is  hardly  in  order  to  call  a 
9-in. pump  'large'  or  to  consider  it  or  its  valves  difficult  of  operation" 
scarcely  calls  for  comment. 

It  is  safe  to  say  that  where  a  48-in.  pump  is  regularly  used 
for  dredging  sand,  it  is  not  used  in  connection  with  a  nest  of  48-in. 
valves. 

Mr.  Lamb  asks  why  a  gravity  plant  could  not  be  placed  at 
the  Liberty  Bell.  The  answer  is,  for  the  same  reason  probably 
that  it  was  not  installed  at  Millers.  It  would  cost  more  to  ex- 
cavate for  it  than  it  would  be  worth. 

In  a  personal  letter,  Mr.  F.  L.  Bosqui  has  pointed  out  wherein 
my  former  article  was  seriously  incomplete,  by  not  giving  com- 
parative cost  data  for  filter-repairs  and  maintenance,  for  the  But- 


230  RECENT  CYANIDE  PRACTICE. 

ters  and  Moore  systems.  Mr.  Bosqui's  criticism  is  entirely  just. 
I  could  not  give  these  data,  as  I  have  not  got  them.  Such  as  I 
have  on  the  Moore  process,  are  vitiated  by  two  factors,  namely: 
At  Bodie,  the  plant  was  run  several  weeks  without  re-grinding, 
and  the  heavy  sand  rapidly  cut  the  filters  to  pieces,  and  raised  the 
costs  materially  for  the  period  covered  by  the  data  I  have.  At 
the  Liberty  Bell,  the  niters  are  being  changed  as  rapidly  as  may  be 
to  a  better  type,  in  part  similar  to  the  ones  at  Bodie,  and  re- 
pairs make  consequently  a  large  item.  Experience  seems  to  in- 
dicate, though,  that  filter-repairs  are  less  for  the  Butters  than 
for  the  Moore  process. 

EDWARD  H.  NUTTER. 
Telluride,  January  30. 


CYANIDATION  AT  COPALA,  MEXICO 

(March  16,  1907) 

The  Editor: 

Sir — Enclosed    please    find    diagram   which    is  self   explana- 
tory.    It   was   prepared  for  the  purpose   of   comparing    quickly 


FOUR  PPff  BOXES. 
Value  efZn.  per  02  bullion^  *  O.  O/3 
Labor,  including  cost  of  cleaning  totes, 
filter-press  and  jcre«n/rjg,per  oz. 6u//ion*$O.OO/8 


TT£f!S"E)(TERNALLY-nr?ED  HOT-AIR  DRYER 
Cost  ofdr(/inffper0z.t>u///on-  &O.OOO9 


FL  C/X//VG  /WD  MIXING  BOX 


"F.W.BRAU/i  HAND- POWER  BRlQUETTING/WCHf HE 
Cosf  of  flux,  mining  and  briquettingper  oz,  bv/lion-$O.OO/9 


'EL  ORO'MODEL  COKE-BURNING 
WIND  FURNACES  -  /V93OO  CRUCt&LES 

Cost  sme/t/ng  and  refining  per  oz.  bullion-  *O.O/8 


fl//  computations  //?  Mexican  currency 
Total  '  cojf  //i  yo/d  currency  of  prectp'Catio/i 
melting,  re  fining  ano"  dressing  •  &O.O/7Q  per  oz. 


Copala.  Dec.  <?J  <-'O6 


Fig.  28. 

costs  at  the  various  stages  and  also  to  graphically  describe  the 
present  system  and  compare  it  with  others  which  have  preceded 


232  RECENT  CYANIDE  PRACTICE. 

it.  You  will  notice  that  the  acid  treatment  is  entirely  dispensed 
with,  all  zinc  shorts  being  returned  to  the  head  sections  of  the  boxes, 
not  only  affording  us  a  marked  saving  in  zinc  consumed,  but  also 
greatly  simplifying  the  process  and  saving  us  the  cost  of  acid, 
extra  filter-press,  acid-pump,  etc. 

The  precipitation  boxes  are  of  eight  compartments  with 
bottom-discharge  valves.  The  slime  is  run  into  a  screening  tank 
through  a  No.  30  screen.  The  tank  is  made  in  two  compartments, 
separated  by  a  vertical  division  having  its  top  six  inches  below 
the  upper  rim  of  the  tank,  so  that  when  the  first  division  is  full 
the  product  overflows  into  the  second  (leaving,  of  course,  nearly 
all  the  precipitates  in  the  first  section)  and  is  then  pumped  through 
the  filter-press.  Both  divisions  have  bottom  connections  to  the 
filter.  This  arrangement  allows  the  cleaning  of  all  the  boxes 
without  interruption,  for,  as  we  very  frequently  get  more  than  a 
cake  of  precipitate  in  three  of  the  four  boxes  and  as  we  have  to 
clean  all  of  them  daily,  without  this  device  we  wrould  be  compelled 
to  empty  the  filter  before  we  could  complete  the  boxes.  Of  course, 
we  open  up  the  suction  to  the  first  section,  when  we  are  ready  to 
make  cake. 

The  precipitate,  which  contains  from  18  to  20%  moisture, 
then  goes  to  the  dryer  and  the  moisture  is  reduced  to  5%.  This 
dryer  consists  of  an  iron  cylinder  30  ft.  long  by  30  in.  diam. 
having  an  external  fire-box,  which  allows  a  uniform  heating. 
A  car  24  ft.  in  length  and  holding  six  portable  steel  trays,  contain- 
ing the  precipitate,  is  run  in  on  a  track  that  also  extends  a  like 
distance  outside  the  shell  to  allow  easy  handling  of  the  product. 
There  is  a  vent  at  the  far  upper  extremity  of  the  shell  to  carry  off 
steam,  etc.,  and  the  entrance  is  closed  with  a  steel-hinged  door. 
This  device  has  given  every  satisfaction,  being  effective  and  econom- 
ical. 

The  precipitate  then  goes  to  the  mixing-box,  where  the  flux 
and  binder  are  thoroughly  incorporated  and  pressed  into  briquettes, 
which  are  then  ready  for  the  crucible.  Only  the  No.  300  crucible 
is  used,  and  a  unit  charge  consists  of  220  Ib.  precipitate  with  its 
flux.  As  the  briquettes  melt  down,  more  are  added,  until  the 
crucible  has  its  full  charge.  There  is  no  dusting.  Four  thousand 
three  hundred  ounces  are  refined  as  a  charge  and  four  charges  are 
run  in  the  same  crucible  within  seven  and  one-half  hours.  Dip 
samples  are  taken. 


CYANIDATION  AT  COP  ALA,  MEXICO.  233 

The  briquetting  machine  is  manufactured  by  the  F.  W. 
Braun  Co.  and  is  really  intended  for  the  manufacture  of  cupels. 
But  with  a  square  mold  and  die,  2^  by  2  by  1J  in.,  it  makes  a  clean, 
hard  cake  and  will  handle  about  100  Ib.  per  hour. 

The  precipitation-boxes,  screening.-tank,  filter-press,  and 
briquetting-machine  are  so  placed  as  to  allow  a  solid  concrete 
floor  draining  to  a  small  pump  near  the  filter.  The  entire  floor 
is  thoroughly  washed  with  a  hose  every  evening  and  by  a  simple 
bye-pass  on  the  suction  this  water  is  pumped  through  the  press. 
The  building  is  of  brick,  with  white  plaster  walls  extending  to 
within  four  inches  of  the  floor,  where  there  is  a  cement  collar. 
This  makes  it  easy  to  detect  any  carelessness  in  handling  the 
product. 

The  staff  consist  of  one  white  foreman  and  five  native  boys. 
On  account  of  the  high  charges  for  freighting  between  Mazatlan 
and  the  mines,  coke  costs  us  69  pesos  per  ton;  fluxes,  zinc,  crucibles, 
etc.,  are  proportionately  high,  so  that  taking  everything  into  con- 
sideration the  cost  per  ounce  is  extremely  low.  We  handle  on 
an  average  about  three  tons  of  precipitate  per  month. 

Although  this  method  is  far  from  new,  I  think  there  are  two 
or  three  features  of  it  that  are  certainly  not  in  general  use,  namely: 

1.  Returning  all  zinc  shorts  to  boxes  and  thus  entirely  dis- 
pensing with  acid  treatment. 

2.  Briquetting  product  with  flux  incorporated  and  smelt- 
ing same  without  re-drying  (they  average  5%  moisture). 

3.  The  refining  of  the  bullion  in  large  crucibles,  making  unit 
charges  of  four  and  five  1,000-oz.  bars. 

The  first  has  been  in  successful  operation  for  ten  months. 
By  first  laying,  say,  two  inches  of  long  zinc  on  the  trays  of  the 
first  section  of  the  precipitation-boxes,  then  lightly  laying  the 
short  zinc  on  top  to  a  depth  of  1£  in.  and  alternating  this  until 
the  section  is  half  filled,  and  finally  filling  entirely  with  carefully 
placed  long  zinc,  we  have  attained  the  desired  result.  All  the 
zinc  is  consumed  and  precipitation  is  perfect. 

The  briquetting  partly  does  away  with  the  expense  of  calcin- 
ing, as  the  product  is  dried  to  only  5%  moisture.  This  product  is 
in  every  way  safer  and  cleaner  to  handle  and  there  is  no  spitting 
or  dusting  of  the  product  in  the  crucibles.  The  capacity  of  the 
latter  is  likewise  greatly  increased,  unless  the  comparatively  un- 
safe practice  of  adding  the  dry  calcined  powder  to  same  is  followed, 


234  RECENT  CYANIDE  PRACTICE. 

which,  even  when  the  paper  bags  are  used,  allows  more  or  less 
loss  by  dusting,  etc.  In  the  case  of  briquettes  we  add  to  the  cru- 
cible without  any  danger  until  it  is  as  full  as  desired. 

Mr.  Edwin  Burt,  superintendent  of  cyaniding  for  El  Oro 
Mining  &  Railway  Co.,  Ltd.,  will  bear  me  out  in  all  of  the  above, 
as  it  was  he  who  first  put  it  into  practice  in  Mexico,  inventing  his 
own  briquetting-machine,  a  very  ingenious  device;  the  above- 
mentioned  company  also  now  briquettes  all  of  its  product. 

As  for  No.  3,  this  means  less  work  and  a  very  large  saving  in 
fuel. 

I  shall  finish  by  saying  that  the  practice  here  is  very  satis- 
factory, the  equipment  is  complete,  and  the  results  are  certainly 
economical.  It  is  hoped  that  you  will  make  use  of  whatever 
you  see  in  this  short  sketch  that  may  prove  of  value  to  others, 
and  I  shall  be  glad  to  read  any  discussion  on  the  subject. 

LAURENCE  N.  B.  BULLOCK. 

Copala,  Sinaloa,  Mexico,  January  12. 


THE  BUTTERS  FILTER 

(March  23,  1907) 

The  Editor: 

Sir: — The  discussion  in  regard  to  the  Moore  and  Butters 
filter-processes  has  become  most  interesting  to  me  and  probably 
also  to  others  interested  in  the  treatment  of  slime.  The  following 
data  may  be  of  use  to  the  profession;  they  refer  to  the  Combina- 
tion mill  at  Goldfield,  Nevada. 

The  tanks  and  apparatus  in  use  are  as  follows:  Two  slime 
storage  vats,  two  wash- water  vats,  the  filter  box  and  canvas 
frames,  one  acid-box  for  the  washing  of  frames,  one  vacuum- 
pump,  one  four-inch  Butters  centrifugal  slime  pump,  one  two- 
inch  Krogh  centrifugal  pump,  valves,  and  piping. 

The  pulp  after  agitation,  containing  60%  of  a  1.5-lb.  solu- 
tion of  cyanide,  is  discharged  into  the  slime-storage  vats  (13.65 
ft.  diam.  by  12  ft.  high  with  slightly  conical  bottoms)  ready  for 
the  filter-box.  Two  of  these  vats  are  in  use,  each  one  containing 
a  mechanical  stirring  apparatus  with  paddles,  keeping  the  pulp 
of  the  same  consistence  throughout.  One  vat  of  this  capacity 
will  easily  hold  three  charges  for  the  filter-box  (the  size  of  which 
is  specified  further  on),  and  the  two  used  in  conjunction  will  hold 
about  eight  charges,  all  depending  on  the  thickness  of  the  pulp 
and  cake  to  be  formed. 

The  storage- vats,  filter-box,  wash-water  vats,  and  vacuum 
pump  are  all  on  the  same  level.  The  pump  used  in  connection 
with  the  filter-box  is  placed  about  six  feet  below  the  vats,  which 
simplifies  the  piping  and  operation  of  the  valves.  This  four- 
inch  centrifugal  pump  (patented  by  Mr.  Butters)  is  especially 
adapted  to  the  handling  of  pulp  containing  slime  or  fine  sand,  and 
has  given  little  trouble  to  the  operator  or  mechanic;  it  is  the 
least  troublesome  pump  in  the  mill. 

The  inside  top  measurements  of  the  filter-box  are  9  ft.  11J  in. 
by  10  ft.  2J  in.,  the  sides  extend  5  ft.  9^  in.  above  the  cone,  and 
from  the  discharge  gate  to  the  top  is  just  11  ft.  7f  in.,  with  a  capac- 
ity of  about  785  cu.  ft.  when  not  containing  the  frames.  The 
frames  are  116J  by  56J  in.,  each  having  about  90  sq.  ft.  of  filter- 
ing surface.  There  are  27  of  these  frames;  six  sets  of  four,  and 


236  RECENT  CYANIDE  PRACTICE 

one  of  three.  The  four  frames  are  connected  at  the  bottom  by 
f-in.  rubber  hose  with  the  use  of  J-in.  iron  nipples  and  Ts.  Each 
set  is  connected  by  f-in.  iron  piping  from  the  connection  on  the 
frames  through  the  side  of  filter-box  to  the  main  (pipe  on  the  out- 
side) leading  to  the  vacuum-pump.  It  may  be  mentioned  here 
that  the  connecting  of  the  frames  to  the  vacuum-pump  should  be 
at  the  top,  in  order  to  be  convenient  to  get  at  whenever  necessary 

About  35  tons  of  slime  are  treated  daily  at  this  plant,  form- 
ing a  f-in.  cake  on  the  filters  with  a  22-in.  vacuum  and  washing 
with  the  same  amount  of  vacuum  for  from  70  to  80  minutes  with  a 
weak  solution  of  cyanide  (0.8  lb.),  using  about  10  tons  of  wash 
solution  in  that  time. 

Water  is  scarce  in  southern  Nevada.  If  water  could  be  used 
in  the  washing  of  the  cakes,  the  time  consumed  would  be  about 
two-thirds  that  required  with  the  use  of  a  cyanide  solution.  Also 
if  the  slime  could  be  agitated  or  treated  in  just  twice  as  much  solu- 
tion as  is  used  at  present,  necessitating  less  time  of  agitation  and 
giving  the  same  result,  it  would  require  still  less  time  in  washing 
the  cake.  The  slime-treating  capacity  is  now  being  enlarged 
for  this  purpose. 

A  record  was  kept  of  the  charges,  in  regard  to  the  time  in 
forming  cake,  pumping  of  pulp  in  or  out  of  box,  thickness  of  cake, 
etc.  The  following  is  taken  from  these  records  when  the  plant 
was  first  installed : 

Minimum  time.      Maximum  time 
Minutes.  Minutes. 

Filling  of  box  with  pulp 16  18 

22-in.  vacuum,  while  forming  f-in.  cake 19  22 

Emptying  box  with  5-in.  vacuum  on  cakes 16  17 

Pumping  in  weak-solution  wash 15  16 

Washing  with  weak  solution,  15-in.  vacuum.  ...  40  50 

Pumping  back  weak  solution 15  16 

Filling  with  wash-water 15  16 

Washing  with  wash-water,  22-in.  vacuum 30  50 

Sampling  cake 7  10 

Dropping  cake  with  water 12  14 

Running  back  surplus  water 8  10 

Sluicing 5  7 

Total  .  ..198  246 


Five  months  later  when  carbonate  of  lime  became  noticeable 
and  with  increased  amount  of  slime  in  the  pulp,  the  figures^were: 


THE  BUTTERS  FILTER.  237 

Minimum  time.      Maximum  time. 
Minutes.  Minutes. 

Filling . 18  20 

Vacuum 22  25 

Emptying  with  3-in.  vacuum  on  cake 17  20. 

Pumping  in  wash 16  18 

Washing  with  22-in.  vacuum 70  80 

Sampling  cake 7  10 

Dropping  cake 14  15 

Running  back  water 8  10 

Sluicing 5  7 

Total 177  205 

You  will  notice  that  two  washes  were  used  when  the  plant 
was  first  installed,  but  later  only  one.  The  reason  for  this' change 
was  the  increased  amount  of  slime;  the  saving  of  time;  the 
exposure  of  the  cakes  the  second  time  for  so  long  to  the  air,  causing 
them  to  crack;  the  wash- water  often  contained  as  much  cyanide 
as  did  the  weak  wash  and  the  second  process  gave  better  re- 
sults. 

At  first,  when  the  canvas  was  new,  while  pumping  the  sur- 
plus pulp  out  or  wash-water  into  the  box  after  the  cakes  had 
been  formed,  a  vacuum  of  five  inches  was  left  on  the  frames, 
this  being  just  enough  to  keep  the  cakes  from  slipping  off  and 
not  enough  to  dry  or  cause  cracking,  but  I  found  as  the  carbonate 
of  lime  began  to  form  on  the  canvas  (and  where  only  the  dipping 
of  the  frames  in  hydrochloric  acid  was  resorted  to)  that  five  inches 
was  too  much  vacuum  and  caused  the  cakes  to  dry  and  crack, 
but  three  inches  proved  more  satisfactory. 

After  the  washing  of  the  cakes  they  are  dislodged  from  the 
frames  by  water  forced  from  the  inside.  The  surplus  wash- water 
is  run  back  to  the  storage-vat  by  gravity  and  only  that  water 
(4J  to  5J  tons,  depending  on  the  amount  of  associated  washed 
slime)  remaining  in  the  cone  of  the  box  is  lost,  which  -is  neces- 
sary in  sluicing  the  slime  away  through  an  8-in.  quick-opening 
gate-valve. 

Very  little  has  been  said  heretofore  about  the  carbonate 
of  lime  forming  on  and  in  the  filters,  which  in  my  opinion  is  quite 
an  essential  obstacle  to  be  got  rid  of.  Although  somewhat  simple, 
it  is  a  necessary  feature  in  the  successful  operation  of  the  process, 
and  it  cannot  be  accomplished  by  simply  dipping  the  frames  in  a 
2%  solution  of  HC1  and  water  where  any  large  amount  of  lime 
is  used  in  the  milling  of  the  ore,  say  from  7  to  20  Ib.  per  ton.  It 


238  RECENT  CYANIDE  PRACTICE. 

must  be  accomplished  by  washing  with  the  use  of  vacuum,  or  any 
other  means  that  either  forces  or  draws  the  dissolving  2%  solution 
of  HC1  acid  through  each  cell  of  the  cocoa-matting  for  15  to  45 
min.  If  this  process  is  used,  the  frames  will  only  have  to  be  sub- 
jected to  the  wash  once  in  three  or  four  months,  depending 
on  the  amount  of  lime  in  use,  whereas  the  dipping  operation 
would  have  to  be  done  at  least  once  in  two  or  three  weeks  and 
then  it  would  be  very  unsatisfactory. 

Although  a  small  formation  of  lime  on  the  filters  does  not 
seem  either  to  interfere  with  the  washing  of  the  gold  from  the 
cake  or  to  diminish  the  net  extraction,  it  greatly  prolongs  the 
operation  and  reduces  the  capacity  of  the  plant. 

One  cubic  foot  of  dry  Combination  slime  weighs  76  Ib.  or 
thereabout,  while  160  Ib.  in  water  only  occupies  one  cubic  foot. 
It  was  found  that  one  square  foot  from  a  -f-in.  cake  contained 
5.03  Ib.  dry  slime  and  28%  moisture,  so  calculating  from  these 
results,  in  forming  a  f-in.  cake  you  would  be  treating  6.11  tons  of 
dry  slime  per  charge.  But  from  a  larger  test  we  found  that  6.76 
tons  were  treated  in  forming  a  j-in.  cake,  due  to  the  greater 
thickness  of  the  cake  at  the  bottom  of  the  frame. 

Now,  I  think  I  shall  be  stating  the  truth  when  I  say  that  in  a 
plant  of  this  size  and  design,  when  filters  are  kept  free  from  CaCO3, 
by  washing  for  70  min.  you  can  treat  50  tons  of  slime  (having  the 
same  characteristics  as  that  produced  in  the  Combination  mill) 
in  every  24  hours,  counting  all  delays,  with  the  use  of  a  15-h.p. 
induction  motor  operating  two  mechanical  agitators,  one  vacuum 
pump,  one  4-in.  centrifugal  slime-pump,  and  three  2-in.  centrif- 
ugal pumps. 

One  man  per  shift  of  eight  hours  can  easily  operate  the  valves 
from  a  platform  near  the  filter-box,  and  have  plenty  of  time  for 
other  mill-work. 

The  Butters-Cassel  process  for  filtering  slime  is  certainly 
a  great  improvement  over  all  other  processes  and  as  an  invention 
it  ranks  with  the  tube-mill  in  importance. 

E.  S.  PETTIS. 

Denver,  February  28. 


TUBE-MILL  LINING 

(March  30,  1907) 

The  Editor: 

Sir — The  experience  of  Mr.  A.  E.  Drucker,  in  Korea,  as  given 
in  your  issue  of  November  17,  1906,  is  interesting.  To  my  mind, 
the  reasons  why  he  obtained  such  very  unsatisfactory  results 
in  his  ingenious  experiment  are  the  following : 

1.  His   mill   is   probably  too   light    in    construction,    thus 
allowing  the  lining  to   'work.'  ,  Any  continuous  bonding  move- 
ment in  the  walls  of  his  mill  must  gradually  break  up  his  lining, 
which  is  in  one  continuous  length. 

2.  I  think  it  was  a  mistake  to  make  the  lining  in  two  distinct 
layers  and  to  cover  the  tops  of  the  rails. 

In  reference  to  my  'honeycomb'  linings  which  he  refers  to 
as  'proposed  to  be  used,'  I  can  assure  him  there  is  no  doubt  about 
the  matter,  they  have  actually  been  in  use  for  over  a  year,  showing 
over  three  times  the  life  of  imported  silex.  Nine  tube-mills 
are  now  running  in  Waihi  with  my  patent  linings. 

By  dividing  up  the  spaces,  as  I  do,  the  lining  material  has  not 
the  same  chance  of  working  loose  as  in  the  method  tried  by  Mr. 
Drucker.  He  is  quite  right  in  saying  that  no  cement  will  stand 
the  terrific  wear,  but  it  only  wears  to  a  certain  depth,  when  it 
becomes  protected  by  the  quartz  projecting  around  it.  If  Mr. 
Drucker  has  a  foundry  handy  I  am  sure  he  will  find  it  worth  while 
to  try  my  system,  as  his  only  difficulty  seems  to  be  in  holding 
the  quartz  in  position  and  not  in  the  wearing  quality  of  the  quartz 
lining. 

H.  P.  BARRY. 

Waihi  Gold  Mining  Co.,  Ltd.,  Waihi,  New  Zealand,  Feb- 
ruary 1. 


ASSAY  OF  CYANIDE  SOLUTIONS 

(March  30,  1907) 

The  Editor: 

Sir — Will  you  kindly  publish  the  following  scheme  for  the  assay 
of  cyanide  solutions ;  it  is  a  modification  of  Crosse ;  it  is  quick  and 
accurate,  does  away  with  the  tedious  evaporation,  and  chance  of 
loss,  and  the  furnace. 

Measure  30  c.c.  KCy  (working  solution),  add  silver  nitrate 
solution  used  ordinarily  in  titrating,  until  precipitate  ceases  to 
form;  the  gold  is  all  now  precipitated  as  argenti-auric  cyanide. 

Allow  precipitate  to  settle;  decant  clear  solution,  then  with 
wash-bottle  transfer  precipitate  into  small  funnel,  using  thin  paper; 
wash  several  times  to  get  precipitate  well  down  into  point  of  paper; 
draw  out  paper  and  cut  off  jufct  above  the  precipitate;  place  this 
cone  into  a  hole  cut  in  charcoal,  blow-pipe,  flatten,  part,  anneal, 
and  weigh. 

H.  W.  GENDAR. 

Ballarat,  Cal.,  March  5. 

[Many  thanks.     Such  hints  are  useful. — Editor.] 


THE  BUTTERS  FILTER 

(March  30,  1907) 

The  Editor: 

Sir — As  Mr.  Nutter  says,  in  your  issue  of  February  16,  the 
data  given  in  my  former  criticism  were  not  taken  from  the  plant 
at  Millers,  since  at  the  time  of  my  visit  to  that  camp,  the  plant  was 
not  in  operation. 

I  am  glad  to  get  the  data  supplied  by  Mr.  Nutter,  and  knowing 
the  possibilities  of  the  filter,  I  feel  sure  that  the  results  now  being 
attained  by  Mr.  Parsons  will  shortly  be  even  better. 

My  error  in  regard  to  the  number  of  filter-leaves  at  Millers 
was  due  to  the  fact  that  216  leaves  were  billed  to  the  company. 
I  presume  that  it  has  been  found  that  less  leaves  will  treat  their 
slime.  I  should  perhaps  have  said  tjiat,  "a  plant,  designed  accord- 
ing to  my  ideas,"  instead  of  "a  properly  designed  plant,"  would 
be  arranged  for  a  maximum  lift  of  10  ft.  I  enclose  a  tracing 
covering  this  point.  The  average  lift  is  of  course  much  less,  varying 
from  minus  10  to  plus  10  ft.  This  is  Mr.  Bosqui's  arrangement 
at  the  Combination  mill  at  Goldfield,  Nevada.  The  actual  maxi- 
mum lift  varies  from  hour  to  hour,  depending  on  the  stage  of  the 
tide  in  the  various  tanks  of  pulp,  solution,  and  water.  It  it 
therefore  clear  that  any  construction  entailing  a  maximum  lift 
of  25  ft.  will  necessitate  large  pumps  (or  more  time)  and  more 
power.  The  tracing  sent  you  is  wrong  in  showing  the  discharge 
from  the  pump  to  the  wash-solution  tank  as  going  over  the  top  of 
the  tank.  This  should  be  connected  to  the  tank  below  the  low- 
water  level.  It  will  be  easily  seen  from  this  drawing  that  the 
greatest  possible  lift  would  occur  in  returning  pulp  or  solution, 
with  the  storage-tanks  full  at  the  moment  that  the  filter-box  was 
empty.  This  tank  is  10  ft.  higher  than  the  outlet  of  the  filter-box, 
and  I  am  unable  to  see  any  advantage  to  be  gained  by  increasing 
this  height.  The  same  arrangement  can  be  applied  to  a  plant  of 
whatsoever  size. 

As  regards  the  cubic  capacity  of  the  filter-box,  I  must  explain 
that  this  depends  upon  the  spacing  of  the  leaves,  and  this  spacing 
depends  upon  the  nature  of  the  slime  treated.  As  an  example, 
experiments  are  being  made  upon  slime  here  in  Guanajuato  of 


bo 


bo 


244  RECENT  CYANIDE  PRACTICE. 

which  a  cake  1J  in.  thick  forms  with  a  22  in.  vacuum  in  30  min. 
This  slime  necessitates  a  spacing  of  five  or  more  inches  (instead  of 
four).  The  filter-box  for  this  slime  will  be  5  ft.  10  in.  from  the  top 
of  the  filter-leaves  to  the  hopper,  and  the  latter  will  be  6  ft.  3  in. 
deep.  I  repeat  that  for  250  leaves  for  slime  ordinarily  produced  in 
milling,  a  Butters  filter-box  should  not  exceed  7,000  cubic  feet. 

As  regards  the  time  and  size  of  pump  necessary  for  trans- 
ferring pulp  and  water,  and  taking  Mr.  Nutter's  figure  of  1,900 
cu.  ft.  as  the  displacement  of  the  loaded  leaves,  5,100  cu.  ft.  of 
pulp  would  have  to  be  transferred.  A  10-in.  pump  (I  have  no 
data  on  hand  on  the  capacity  of  a  9-in.  pump)  would  actually 
require  "according  to  the  manufacturer"  7.5  min.  and  15  h.p. 
to  do  this. 

As  regards  filter  repairs,  it  is  hardly  putting  it  strongly  enough 
(in  view  of  the  fact  that  Butters  filter-leaves  have  been  in  operation 
over  two  years  without  any  signs  of  deterioration)  to  merely  say  that 
filter  repairs  are  "less"  for  the  Butters  than  for  the  Moore  process. 
One  of  the  great  points  of  superiority  of  the  Butters  method  is 
that  the  leaves  hang  perfectly  still,  and  are  subject  to  no  strains, 
are  not  scraped  (as  are  the  "better  type  at  Bodie")  or  even  touched 
for  months  at  a  time. 

As  a  point  of  interest,  I  may  state  that  the  filter  now  being 
constructed  for  the  Pinguico  mill  of  this  place,  is  designed  on 
"gravity"  lines,  as  illustrated  in  your  issue  of  recent  date,  and  not 
"all  pumping;"  and  in  this  case  (where  the  filter  is  filled  and  emptied 
by  gravity,  and  the  pulp  returned  from  a  low  sump-tank)  their 
maximum  lift  will  not  exceed  30  feet. 

I  must  not  be  suspected  .of  being  convinced  of  the  merits 
of  the  Butters  filter  on  account  of  being  interested  in  its  success — 
rather  the  contrary,  having  become  interested  after  conviction  as 
to  its  merits. 

MARK  R.  LAMB. 

Guanajuato,  Mexico,  March  6. 

[Having  been  favored  by  Mr.  Lamb  with  a  copy  of  the  fore- 
going contribution,  Mr.  E.  H.  Nutter  writes  to  say  that  "the  filters 
at  Bodie  have  not  been,  and  are  not,  scraped  in  order  to  clean 
off  the  cake.  The  discharge  is  accomplished  entirely  by  blowing 
the  cake  off  with  compressed  air,  as  stated  by  Mr.  R.  Oilman 
Brown  in  an  earlier  article." — Editor.] 


PANS  V.  TUBE-MILLS 


(April  6,  1907) 

The   Editor: 

Sir— With  reference  to  the  discussions  that  have  appeared 
in  the  MINING  AND  SCIENTIFIC  PRESS  regarding  the  relative  merits 
of  pans  and  tube-mills  as  sliming  machines,  it  may  be  of  interest 
to  publish  the  results  of  some  tests  carried  out  at  the  Dolores  mill, 
in  Chihuahua,  Mexico. 

In  test  No.  1,  the  ore  was  crushed  with  cyanide  solution  by 
15  stamps,  weighing  900  lb.,  through  a  2-mesh  screen,  the  pulp 
passing  to  the  two  Bryan  mills  with  60-mesh  screens,  then  to  four 
pans  in  series,  thence  through  two  settlers,  and  finally  through 
two  cone-classifiers.  The  overflow  from  the  classifiers  went  to 
the  agitation  plant,  and  the  underflow  was  returned  to  the  tube- 
mill  for  re-grinding,  the  re-ground  product  joining  the  stream 
from  the  settlers  at  the  head  of  the  cones. 

In  test  No.  2,  the  pulp  from  the  Bryans  passed  directly  to 
the  tube-mill,  thence  to  the  cones,  the  overflow  as  before  to  the 
agitation  plant,  the  underflow  being  returned  to  the  head  of  the 
pan  series,  thence  through  settlers  to  cones  as  before. 

In  both  tests  samples  were  taken  every  hour,  over  periods 
of  twelve  hours,  from  the  heads  of  the  tube-mill  and  heads  of  pans, 
and  also  from  the  discharge  of  same.  The  bulk  12-hour  samples 
was  determined  from  the  proportion  of  sand  and  slime  in  each 
sample,  the  difference  in  slime  content  between  heading  and  tailing 
being  taken  as  the  sliming  power  of  each  machine. 

The  following  are  the  results  obtained,  from  the  average 
of  five  samples: 

TEST   NO.  1. 


Percentage 
of  slime. 

Tube-mill  heading 8 . 20 

"  tailing 42.64 


Percentage 
of  slime 

Pan  heading 1 1 . 02 

"    tailing 52.54 


Slimed  by  tube  mill 34 . 44    j  By  pans 41 . 52 


TEST   NO.  2. 


Percentage 
of  slime. 

Tube-mill  heading 4.66 

"       "  tailing  ..  .44.08 


Slimed  by  tube-mill 39 . 42 


Percentage 
of  slime. 

Pan  heading 7.36 

"     tailing 51.88 


By  pans 


44.52 


246  RECENT  CYANIDE  PRACTICE. 

Taking   an    average   of   both    tests,   to  bring  the  machines 
under  the  same  conditions,  gives  the  following  result : 


in  favor  of  pans 6 . 09 

The  pans  used  are  of  the  Wheeler  type,  with  plain  flat  muller 
and  dies;  they  have  a  diameter  of  five  feet.  The  speed  is  65  rev. 
per  minute.  The  power  required  to  drive  the  four  pans  is  50  h.p. 
The  tube-mill  is  a  machine  specially  constructed  by  Allis- 
Chalmers,  made  in  sections  for  mule  transport,  and  I  believe 
is  one  of  the  first,  if  not  the  first,  sectional  tube-mill  made.  It  has 
a  length  inside  of  16J  ft.  by  3  ft.  6  in.  diam.,  and  runs  at  a  speed 
of  35  revolutions.  It  is  lined  with  white  iron,  and  carries  a  load 
of  4J  tons  of  flint  pebbles.  The  power  required  to  drive  it  is  20 
horse-power. 

Although  the  above  tests  showed  a  small  margin  in  favor 
of  the  pan  for  sliming,  yet  when  the  question  of  power  and  cost 
are  considered  the  tube-mill  is  undoubtedly  the  more  economical 
machine.  The  wear  and  tear  in  the  case  of  the  pans  is  consider- 
ably more  than  that  of  the  tube-mill,  and  the  difference  in  power 
required  for  driving,  by  itself  would  more  than  minimize  any 
advantage  the  pans  have  in  sliming  capacity. 

ROBERT  CLARKE. 

Dolores,  February  17. 


THE  TREATMENT  OF  DESERT  ORES 

(April  28,  1907) 

The  Editor: 

Sir — Referring  to  Mr.  Bosqui's  recent  article  on  this  subject, 
although  in  the  typical  oxidized  gold  ore  of  the  desert  regions 
of  Nevada  and  California  the  gold  is  free,  it  is  so  extremely  fine 
and  flaky  that  it  does  not  readily  amalgamate,  but  only  yields  a 
comparatively  small  percentage,  and  treatment  by  cyanide  is 
necessary.  The  present  fashion  of  putting  in  stamp-mills  and 
amalgamating  arrangements  followed  by  a  cyanide  annex  evi- 
dently is  due  solely  to  the  "compelling  power  of  custom,"  and 
not  to  any  proof  that  this  is  the  best  method  of  treating  such  ores. 
To  me  this  looks  like  attempting  to  make  the  ore  suit  the  pro- 
cess, instead  of  suiting  the  process  to  the  ore. 

The  wet  crushing  followed  by  cyanidation  does  not  allow 
the  treatment  by  either  amalgamation  or  cyanide  to  be 
done  under  the  best  conditions.  It  often  happens,  especially 
when  inside  amalgamating  plates  are  used,  that  particles  of  amal- 
gam become  detached  and  are  carried  with  the  pulp  to  the  leach- 
ing vats.  The  gold  in  this  amalgam  is  not  completely  recovered 
in  the  cyanide  treatment,  because  its  solution  is  very  slow  indeed. 
In  fact,  in  practice  none  of  it  is  got.  It  can  only  be  recovered 
after  the  tailing  has  been  allowed  to  weather  for  a  sufficient  time 
to  oxidize  all  the  mercury  to  mercuric  oxide — this  and  the  gold 
being  readily  soluble. 

Further,  the  sand  and  slime  are  received  in  the  cyanide  depart- 
ment in  the  worst  possible  condition  for  treatment,  as  they  con- 
tain a  large  excess  of  moisture  which  has  to  be  displaced  by  cyanide 
solution.  This  occasions  a  mechanical  loss  of  cyanide  and  the 
dissolution  of  the  gold  is  much  slower  than  if  the  material  had  been 
dry  when  brought  in  contact  with  the  cyanide  solution. 

Many  of  these  ores  also  contain  large  amounts  of  hydrated 
silicate  minerals,  such  as  clay  and  talc,  which  have  the  property 
of  becoming  plastic  when  worked  with  water,  yielding  slime 
which  is  difficult  (and  requiring  an  expensive  equipment)  to  treat. 
On  the  other  hand  in  the  dry-crushing  direct-cyanide  method, 
the  material  is  got  in  the  best  condition  for  treatment  by  cyanide. 


248  RECENT  CYANIDE  PRACTICE. 

As  all  the  interstitial  spaces  are  filled  with  air,  the  extraction  of 
the  gold  is  rapid.  In  the  drying  also,  the  hydrated  silicate  miner- 
als are  de-hydrated  and  lose  the  property  of  becoming  plastic; 
therefore  the  subsequent  leaching  is  much  more  cheaply  and  effi- 
ciently done.  Further,  if  the  ore  contains  gold  too  coarse  to  be 
dissolved  in  the  time  of  treatment  allowable,,  the  tailing  can  be 
easily  passed  over  some  amalgamating  device  and  the  gold  (having 
been  cleaned  by  the  cyanide)  will  amalgamate  readily. 

The  use  of  stamp-mills  crushing  in  cyanide  solution  may  be 
satisfactory  in  the  case  of  hard  clean  ores,  but  with  soft  oxidized 
ores,  dry-crushing  is  undoubtedly  the  best.  The  cost  of  installation 
of  a  dry-crushing  direct-cyanide  plant  is  less  than  that  of  a  stamp- 
mill  and  cyanide  annex  and  will  be  found  to  yield  a  higher  profit 
in  the  majority  of  cases.  As  the  majority  of  these  oxidized 
ores  give  a  practically  complete  extraction  by  direct  cyanide 
treatment,  what  is  the  advantage  of  using  both  amalgamation 
and  cyanide  to  recover  the  same  value?  The  removal  of  a  portion 
of  the  gold  as  amalgam  does  not  reduce  the  cost  of  cyaniding  the 
material  appreciably.  The  consumption  of  cyanide  due  to  the 
gold  content  is  negligible. 

In  many  cases  these  surface  desert  ores  are  porous,  so  that  very 
fine  crushing  is  not  needed  and  a  straight  leaching  plant  can  be 
installed  at  a  much  smaller  cost  than  a  stamp-mill  and  cyanide 
annex  of  the  same  capacity.  These  oxidized  surface  ores  are 
called  "free  milling,"  evidently  just  because  they  show  free  gold 
on  panning.  This  is  not  correct.  A  "free  milling  ore"  is  one  that 
yields  a  large  proportion  of  its  gold  to  plain  stamp-mill  amalga- 
mation. In  no  instance  will  these  'free'  desert  ores  yield  any 
large  proportion  of  their  gold  to  amalgamation  but  in  the  majority 
of  cases  the  gold  is  completely  soluble  in  cyanide. 

BERTRAM  HUNT. 

San  Francisco,  April  17,  1906. 


SLIME  FILTERS 

(May  4,  1907) 

The  Editor: 

Sir — I  have  read  with  great  interest  the  contributions  to  your 
columns  regarding  recent  developments  in  slime  filtering.  The 
rivalry  of  the  adherents  of  the  two  most  prominent  systems  of 
vacuum-filtering  should  tend  to  improve  the  practice,  but  I  have 
watched  in  vain  for  a  comparison  of  the  results  attained  here 
with  those  reported  of  the  Ridgway  filter  at  the  Great  Boulder 
mine. 

The  question  at  issue  between  the  Butters-Cassel  and  Moore 
adherents  seems  to  be  as  to  whether  it  is  more  economical  to  install 
and  operate  a  plant  designed  to  transfer  solutions  to  stationary 
filters  or  to  transfer  the  filters  (and  charge)  to  and  from  the  solu- 
tion. As  there  seems  to  be  little  evidence  to  support  the  claims 
of  superiority  in  the  matter  of  attendance  or  speed  of  deposit 
and  washing  the  cake,  in  the  same  slime,  the  discussion  might  be 
said  to  be  narrowed  to  the  comparative  cost  per  ton-capacity 
of  a  plant  of  each  type  capable  of  conducting  the  remaining  opera- 
tions, transferring  and  discharging,  in  a  fixed  time,  with  the  ques- 
tion of  comparative  maintenance  costs  as  a  further  determining 
factor.  Are  there  not  questions  of  more  vital  importance  to  the 
development  of  the  art  ? 

Judging  from  published  reports  on  Moore  and  Butters-Cassel 
installations,  it  appears  that  50  sq.  ft.  of  filter-area  per  ton  of 
slime  (dry  weight)  treated  in  24  hours  is  well  below  the  average 
required.  The  Ridgway  filter,  with  a  total  effective  filter-area 
of  50  sq.  ft.,  is  reported  to  have  a  capacity  of  from  25  to  50  tons 
per  24  hours,  varying  with  the  character  of  the  slime,  or  one  to 
two  square  feet  per  ton  of  slime  treated.  This  comparison  is 
rather  startling  and  suggests  the  necessity  of  a  careful  examina- 
tion of  the  fundamental  elements  of  the  two  plans  of  operation. 
No  conceivable  difference  in  slimes  could  account  for  such  a  wide 
divergence  of  results. 

In  the  American  practice  a  cake  three-fourths  to  one  inch 
thick  is  formed  on  perpendicular  canvas  filters.  In  the  Ridgway 
machine  a  cake  from  three-sixteenths  to  three-eighths  of  an  inch 


250  RECENT  CYANIDE  PRACTICE. 

is  formed  and  suspended  on  a  horizontal  filter-cloth.  The  vacuum 
applied  is  about  the  same,  but  while  the  cake  is  formed  in  13  sec. 
in  the  Ridgway  machine,  from  30  to  60  min.  is  required  in  the 
American  plant.  From  the  nature  of  the  operation  it  is  evident 
that  the  rate  of  accumulation  of  slime  becomes  slower  as  the  thick- 
ness of  the  cake  increases.  The  first  one-eighth  inch  is  deposited 
in  a  much  shorter  period  than  the  last  eighth.  It  is  improbable 
that  the  American  filters  accumulate  from  three-sixteenths  to  three- 
eighths  of  an  inch  of  cake  in  the  first  13  sec.,  but  the  long  time 
required  for  transfers  makes  a  thick  cake  a  necessary  evil. 

The  very  rapid  accumulation  of  the  Ridgway  filters  must  be 
due  to  elementary  differences  that  would  not  appear  of  such  import- 
ance. Is  it  the  difference  in  the  filtering  medium  or  the  position 
of  the  filter?  It  seems  likely  that  filter-cloth  is  so  much  less 
easily  clogged  than  canvas,  that  the  main  difference  in  results 
is  accounted  for  by  this  structural  difference  alone. 

The  results  of  observations  on  the  rate  of  accumulation  of 
the  progressive  layers  of  the  cake,  the  effect  of  position,  horizon- 
tally suspended  or  vertical,  the  rates  of  accumulation  on  canvas 
and  filter-cloth,  and  the  durability  of  filter-cloth  in  horizontal 
and  vertical  positions,  would  be  of  great  assistance  in  improving 
our  practice.  Progress  is  in  the  direction  of  a  compact  automatic 
plant  that  can  be  installed  and  maintained  cheaply.  The  last 
word  has  not  been  spoken  in  the  field  of  vacuum-filtering. 

J.  R.  BLAKE. 

Searchlight,  Nevada,  April  8. 


ASSAY  OF  CYANIDE  SOLUTIONS 

(May  4,  1907) 

The  Editor: 

Sir — I  have  noticed  in  the  PRESS  of  March  30,  Mr.  Gendar's 
scheme  for  the  assay  of  cyanide  solutions. 

I  would  call  the  attention  of  those  interested  to  the  following 
well  known  method,  which,  for  rapid  work  and  accurate  results, 
will,  I.  think,  be  found  to  compare  favorably  with  any. 

Measure,  according  to  grade  of  solution,  a  convenient  quantity 
of  KCy  (working  solution) ,  add  concentrated  sulphuric  acid  to 
excess;  let  stand  two  minutes,  then  add  from  one-half  to  one 
gram  of  cement  copper  and  boil  until  the  solution  takes  on  a  blue 
or  greenish-blue  color,  pour  onto  filter-paper  in  funnel,  wash 
twice  with  boiling  water;  dry  the  filter-paper  containing  the  precipi- 
tate in  air  bath  or  otherwise;  flux  filter-paper  and  precipitate  in 
assay-crucible,  or,  scorify,  cupel,  part,  and  weigh. 

DOUGLAS  MUIR. 

Guanajuato,  Mexico,  April  8. 


SLIME  FILTERING 

(May  11,  1907) 

The  Editor: 

Sir — Seeing  the  necessity  for  a  continuous  filter  in  connec- 
tion with  the  slime  treatment  of  silver  ores,  and  not  finding  any 
reference  in  your  valuable  journal,  I  wish  to  call  your  attention 
and  that  of  some  inventor,  with  means  to  perfect  the  idea,  to 
the  filtering  by  centrifugal  force,  as  in  the  sugar  mills,  with  the 
difference  of  raising  and  discharging  the  cake  over  the  rim  by 
fixed  scrapers,  the  cake  to  fall  into  a  second  centrifugal  machine 
below  the  first,  where  it  is  washed  and  filtered  with  weak  solution 
to  be  finally  discharged  with  water. 

Although  convinced  that  the  ever  alert  inventor  has  this 
idea  near  practical  perfection,  it  would  be  perhaps  a  benefit  to 
the  mining  industry  to  have  it  worked  out  without  patent,  and 
for  this  reason  my  insinuation  in  case  nobody  should  have  taken 
one  on  this  method. 

Please  use  this  to  the  best  of  your  judgment  without  any 
name. 

OLD     SUBSCRIBER. 

Mazatlan,  Mexico,  April  12. 


CYANIDE  PRACTICE  AT  THE  WAIHI 

(May  11,  1907) 

The  Editor: 

Sir — In  your  issue  of  December  15,  1906,  under  the  heading 
'Progress  in  Cyanidation,'  the  statement  is  made  that  "at  the 
Waihi,  treating  25,000  tons  per  month,  it  requires  seven  men 
continuously  to  clean  the  boxes,  using  zinc  shaving." 

This  statement  is  apt  to  convey  a  wrong  impression,  the 
position  being  that  these  men  not  only  clean  the  boxes  weekly 
at  three  separate  plants  cyaniding  a  total  of  27,000  tons  per 
month,  but  also  do  all  work  connected  with  the  acid  treatment 
and  smelting  (weekly)  of  the  zinc-gold  slime,  amounting  to  about 
five  tons  dry  weight  per  month,  and  producing  over  100,000  ounces 
of  bullion. 

E.  G.  BANKS. 

Waihi,  New   Zealand,  March  15. 


METALLURGICAL  DEVELOPMENT  AT 
GUANAJUATO 

BY  T.  A.  RICKARD 

(May  18,  1907) 

It  is  worth  while  to  tell  the  story  of  the  metallurgical  develop- 
ment at  the  Sirena  mill,  more  properly  named  La  Hacienda  San 
Francisco  de  Pastita.  The  successor  to  the  old  patio  was  a  mill 
erected  in  1899;  it  contained  20  stamps,  each  weighing  1,250  Ib. 
The  ore  first  passed  through  a  9  by  15-in.  Blake  crusher  and  was 
then  reduced  to  20-mesh  by  the  stamps,  from  which  it  passed 
to  six  Boss  rapid-grinding  pans.  Here  it  was  re-ground,  so  that 
all  save  5  to  10%  passed  an  80-mesh  screen;  and  then  it  descended 
to  12  more  pans  and  six  settlers.  From  these  the  pulp  went  to 
five  Wilfley  tables.  The  capacity  of  the  mill  was  1,500  to  1,800 
tons  per  month.  The  product  was  amalgam  and  concentrate. 

The  pans  extracted  65%  of  the  assay-value  and  the  concentrate 
contained  12%  more.  This  was  on  the  oxidized  ore.  Although  the 
concentrate  contained  2  kilo,  or  64.2  oz.  silver,  it  barely  paid 
to  send  it  to  market  under  the  smelter  conditions  then  existing 
in  that  part  of  Mexico.  However,  another  factor  came  into  play; 
as  the  lower  workings  were  opened  up,  the  percentage  of  recovery 
by  amalgamation  fell  off  until  it  was  only  60%.  Concurrently, 
the  consumption  of  mercury  and  copper  sulphate  in  the  pans 
increased,  while  the  concentrate  became  richer — five  to  seven  kilo, 
silver  per  ton.  The  method  was  changed;  concentration  was 
made  to  precede  pan  amalgamation. 

By  this  new  arrangement,  the  cost  of  milling  was  reduced 
from  7.86  pesos  to  4.81.  The  concentration  was  carried  further, 
so  that  the  product  contained  10  to  11  kilo,  silver  and  115  grams 
gold  per  ton ;  yet  the  weight  of  concentrate  remained  at  two  per  cent 
of  the  crude  ore.  The  higher  recovery  by  concentration  balanced 
the  lower  yield  by  amalgamation,  the  commercial  result  being 
less  satisfactory  because  the  precious  metals  in  the  form  of  amal- 
gam were  worth  more  than  when  enclosed  within  a  con- 
centrate that  had  to  be  transported  to  a  distant  smelter. 
Moreover,  the  variation  in  smelter  rates  introduced  a  factor  of 
uncertainty. 


METALLURGICAL  DEVELOPMENT.  255 

Extraction  finally  fell  below  60% .  This  suggested  an  increase 
in  the  mill,  so  as  to  lower  the  fixed  charges.  At  this  period  the 
Government  tax  and  the  expenses  in  connection  with  realization 
of  bullion  amounted  to  1 1%  of  its  gross  value.  The  poor  extraction 
and  the  high  imposts  left  but  a  small  margin  of  profit.  A  search 
for  better  metallurgical  treatment  was  undertaken.  The  cyani- 
dation  tests  made  by  Leonard  Holms  in  1901  did  not  seem  to 
justify  turning  to  that  method  at  that  time;  subsequently,  however, 
E.  M.  Hamilton  made  a  new  research  on  a  working  basis,  with 
a  five-ton  plant,  and  he  obtained  encouraging  results.  However, 
nothing  was  done  for  a  year. 

Meanwhile  the  recovery  by  amalgamation  continued  to  dwindle 
and  when  cyanidation  was  recommenced,  there  was  a  fear  lest 
the  further  change  in  the  ore  with  depth  might  affect  extraction 
by  cyanide  as  it  had  done  that  by  mercury.  In  1904,  Bernard 
MacDonald  was  engaged  to  investigate  the  problem,  with  the 
idea,  among  others,  that  the  Hendryx  process  might  be  applied. 
Complete  cyanide  tests  were  made  and  every  kind  of  ore  in  the 
mine  was  tried.  The  results  fully  confirmed  Hamilton's  earlier 
work;  even  on  the  ore  from  the  bottom  of  the  Sirena  mine  it 
was  demonstrated  that  finer  grinding  was  required  and  that  even 
the  concentrate,  if  ground  dry  to  pass  through  200  mesh,  would 
yield  94  to  96%  with  the  use  of  a  2.5%  cyanide  solution — a 
solution  unusually  strong,  but  based  upon  the  relative  proportion 
of  silver  to  be  dissolved.  A  weaker  solution  would  have  done 
better,  as  was  proved  later. 

In  these  tests  a  fresh  solution  was  introduced  each  24  hours 
into  bottles  that  were  agitated  by  being  attached  to  the  periphery 
of  a  slowly  revolving  wheel.  This  failed  to  reproduce  working 
conditions,  because  it  eliminated  a  drawback  inevitable  in  practice 
— that  is,  foul  solutions.  For  this  reason  the  results  were  higher 
than  was  to  be  expected  in  the  mill,  but  they  warranted  the  belief 
that  a  plant  specially  designed  for  the  treatment  of  the  concentrate, 
would  yield  larger  profits  than  the  sale  of  the  concentrate  to  the 
smelters.  The  tests  demonstrated  also  that  the  silver  sulphide 
was  readily  attacked  by  cyanide  when  the  grinding  was  as  fine  as 
200  mesh.  As  yet,  no  plant  has  been  erected  to  treat  the  concentrate, 
but  it  is  likely  that  this  will  be  done. 

In  the  meanwhile — this  was  in  April,  1904 — it    was  decided  to 
erect  the  existing  cyanide  plant,  which  started  to  work  in  May, 


256  RECENT  CYANIDE  PRACTICE. 

1905.  When  concentration  was  made  to  precede  amalgamation, 
the  grinding  in  pans  was  discontinued,  it  being  found  that  amalga- 
mation was  most  effective  in  charges  instead  of  the  continuous 
process.  In  erecting  the  cyanide  annex,  the  only  change  required 
was  to  divert  the  flow  from  the  Wilfley  tables  to  cone-classifiers. 
The  coarse  sand  went  to  a  tube-mill  of  Allis-Chalmers  make,  5  ft. 
diam.  and  22  ft.  long.  It  was  lined  with  chilled  iron,  which, 
after  a  three  weeks'  run,  collapsed,  so  that  the  use  of  the  tube 
stopped  abruptly.  It  has  not  been  employed  since.  Tests  proved 
that  the  benefit  of  the  re-grinding  in  the  tube  hardly  warranted 
the  extra  expense  of  repairs  and  power.  The  first  cone-classifiers 
went  out  of  commission,  the  pulp  going  from  the  Wilfleys  to  a  set 
of  cone-classifiers  that  separate  the  sand  from  the  slime.  The 
arrangement  is  shown  herewith,  in  Fig  1.  A  is  a  large  spitzkasten, 
8  ft.  wide  and  8  ft.  deep,  the  classification  being  by  gravity.  The 
sand,  plus  some  slime,  flows  through  rubber  goose-necks  to  a 
height  two  feet  above  the  bottom  into  four  smaller  cones  or  splitz- 
lutten,  4  ft.  wide  and  4  ft.  deep,  equipped  with  hydraulic  jets. 
The  undersize  from  all  five  cones  unites  to  flow  to  eight  Callow 
steel  settling-cones,  8  ft.  diam.  and  8  ft.  deep,  where  it  is  de-watered. 
Thence  the  pulp  passes  to  three  masonry  vats,  where  lime  is  added 
to  effect  settling  previous  to  decant ation,  at  the  same  time  destroy- 
ing the  acidity  of  the  slime  and  bringing  the  positive  alkalinity 
up  to  1-J  Ib.  lime  per  ton.  Then  this  slime  is  pumped  to  the  treat- 
ment-vats, the  sand  meanwhile  going  to  collecting- vats  from 
which  it  is  taken,  after  draining,  in  cars  to  the  treatment- vats. 

This  was  the  scheme  at  the  commencement  of  cyanidation; 
subsequently  the  masonry  vats,  formerly  employed  in  de- water- 
ing the  pulp  previous  to  pan  amalgamation,  were  modified  so  as 
to  serve  for  holding  and  thickening  the  slime.  The  five  cone- 
classifiers  were  moved  into  the  stamp-mill,  in  order  not  to  lose 
grade,  and  in  this  new  position  they  delivered  direct  into  the 
masonry  vats  behind  the  old  amalgamation  pans,  the  vats  built 
in  the  cyanide  annex  being  used  for  the  same  purpose,  namely, 
to  de-water  the  slime.  Even  now  it  contains  70%  water,  and 
this  70%  is  just  so  much  liquid  that  has  to  be  displaced  by  the 
effective  cyanide  solution,  until  perfect  diffusion  is  attained. 

The  ore  goes  from  the  Sirena  mine  to  the  mill  in  cars  (Kil- 
burn  &  Jacobs)  of  50-cu.  ft.  capacity,  carrying  2.4  tons  each. 
They  have  a  double  side-dump,  with  gable  bottom,  and  appear 


METALLURGICAL  DEVELOPMENT  257 

to  work  easily.  Waste  is  removed  by  sorting  in  the  big  court- 
yard at  the  entrance  of  the  main  adit.  A  sorting  belt  is  to  be 
used  at  the  new  Soledad  shaft,  the  waste  then  eliminated  to  be 
returned  into  the  mine  as  filling.  The  belt  is  to  be  50  ft.  long, 
giving  room  for  five  men  on  each  side  and  illuminated  like  a  bil- 
liard table  by  shaded  electric  lights.  Each  man  is  to  sit  astride 
a  wooden  horse,  which  is  high  enough  to  give  freedom  of  reach 
over  the  belt. 

Gold  can  be  seen  in  the  surface  ores  of  the  Sirena  mine;  it 
accompanies  the  argentite.  Pyrite  does  not  appear  to  be  indic- 
ative, nor  is  it  a  close  associate,  of  the  precious  metals;  it  is  more 
plentiful  in  the  undigested  country  rock.  In  the  ore  of  the  Pere- 
grina  mine  there  is  a  little  arsenical  pyrite  and  also  traces  of  anti- 
monial  silver  minerals.  At  Guanajuato  generally,  the  average 
yield  of  concentrate  does  not  exceed  two  per  cent,  carrying  150 
to  1,600  oz.  silver,  and  from  1  to  30  oz.  gold  per  ton,  so  that  the 
problem  is  to  treat  a  small  quantity  of  high-grade  material,  in 
competition  with  the  expensive  freight  charges  of  the  railroads 
and  the  heavy  treatment  rates  of  the  smelters.  Further,  the 
Government  tax  is  one  per  cent  less  on  bullion  than  it  is  on  the 
precious  metals  when  in  the  form  of  concentrate. 

In  September,  1905,  the  mill  treated  3,887  -tons  of  ore,  con- 
taining 517  gm.  of  silver  and  2.76  gm.  of  gold  per  ton.  On 
leaving  the  concentrators  the  pulp  assayed  302.5  gm.  silver  and 
1.46  gm.  gold.  The  concentrate  recovered  amounted  to  106  tons, 
averaging  948.06  gm.  silver  and  46.92  gm.  gold.  The  cost  of  crush- 
ing and  concentration  amounted  to  1.75  pesos  per  ton.  The 
extraction  by  concentration  was  50.1%  of  the  silver  and  49.1% 
of  the  gold. 

The  practice  is  still  in  course  of  development  and  experi- 
ments are  continually  being  made.  Re-grinding  does  not  seem 
required  by  the  Sirena  ore;  it  is  stamped  through  a  diagonal-slot 
screen  equivalent  to  40  mesh;  a  chuck-block  is  used.  Of  the 
resulting  pulp,  80%  goes  through  100  mesh.  The  granular  quartz, 
when  crushed,  readily  liberates  the  silver  sulphide,  but  the  chalce- 
donic  gangue  in  which  the  silver  occurs  (in  a  cloudy  dissemina- 
tion like  moss  agate),  needs  fine  grinding — all  of  it — to  pass  at 
least  100  mesh.  The  concentrate  carries  30%  silica;  the  portion 
that  passes  through  200  mesh  represents  15.5%  by  weight  and  as 
it  is  worth  398  pesos  per  ton,  it  contains  42%  of  the  assa}'- value 
of  the  ore. 


258 


RECENT  CYANIDE  PRACTICE. 


In  watching  the  agitation  in  the  slime  vats,  it  was  noticeable 
how  the  circular  motion  becomes  accelerated  until  the  moving 
mass  of  pulp  and  solution  moves  faster  than  the  paddles.  On 
starting  the  agitation,  one  can  see  the  sinuous  streaks  of  clear 
cyanide  solution  amid  the  slime,  and  this  condition  of  imperfect 
dispersion  is  never  wholly  overcome;  it  is  due  to  the  resistance  of 
slime  to  diffusion.  I  noticed  this  appearance  (or  phenomenon) 
in  a  vat  that  had  been  at  work  for  40  minutes.  Another  note; 


0 


Q  0 


0 


Fig.  31. 

even  ten  minutes  after  the  agitator  is  stopped  the  movement 
of  water  at  top  of  the  vat  continues  in  the  direction  started  by 
the  paddles.  Two  pounds  of  lime  are  added  per  ton  of  solution 
in  order  to  hasten  settlement  of  the  slime.  The  philosophy  of 
this  has  been  discussed  in  connection  with  milling  at  El  Oro. 

The  loss  of  sodium  cyanide  at  the  Sirena  mill  is  4.12  Ib.  per 
ton  of  crude  ore,  while  the  consumption  of  lime  is  at  the  rate 
of  6  Ib.,  worth  12  pesos  per  metric  ton.  Sodium  cyanide  costs 


bo 


260  RECENT  CYANIDE  PRACTICE. 

$15.75  per  metric  ton  at  Marfil  station,  the  present  terminus 
of  the  Mexican  Central  Railroad  and  to  this  must  be  added  1.25 
pesos,  or,  say  60  cents  for  transport  to  the  works,  making  the  total 
cost  $16.35  per  metric  ton  of  2,204  pounds. 

There  is  always  some  re-precipitation  when  treating  silver 
sulphide,  by  reason  of  the  formation  of  potassium  sulphide,  but 
this  is  diminished  by  the  addition  of  lead  acetate,  which  forms 
a  plumbous  hydrate  that  removes  the  soluble  sulphides  by  forming 
a  lead  sulphide  and  the  potassium  or  sodium  hydrate.  In  prac- 
tice, the  re-precipitation  of  silver  is  surpassed  by  the  re-dissolving 
of  it  in  the  cyanide  solution. 

By  passing  through  cone-classifiers  the  product  escaping  from 
the  upper  mill  is  divided  into  'sand'  and  'slime,'  which  are  treated 
separately,  or  in  the  cyanide  annex.  In  the  'sand'  department 
there  were  20  vats,  each  containing  an  average  charge  of  2,651.7 
cu.  ft.,  or  89.6  tons.  During  the  month  1,792  tons  (dry)  of  sand 
was  treated.  The  average  assay- value  before  treatment  was 
297.5  gm.  silver  and  1.37  gm.  gold;  after  treatment  the  contents 
were  52  gm.  silver  and  0.1  gm.  gold.  In  the  'slime'  department 
there  were  82  vats,  each  containing  3,851.8  cu.  ft.  of  wet  slime, 
equivalent  to  24.26  tons  dry.  During  the  month  1,989  tons  w^ere 
treated.  The  average  assay- value  before  treatment  was  275.5  gm. 
silver  and  1.3  gm.  gold.  After  treatment  the  assay  became  45.5 
gm.  silver  and  0.1  gm.  gold.  The  extraction  was  85.1%  as  regards 
the  silver  and  70%  of  the  gold  in  the  pulp  treated  by  the  cyanide 
annex,  the  total  recovery  by  cyanidation  being  41%  of  the  assay- 
value  of  the  crude  ore,  so  that  the  combined  extraction  by  cyani- 
dation and  concentration  was  91.2  per  cent.  The  total  cost  of 
cyanidation  was  $4.13,  and  the  consumption  of  cyanide  1.9  kilo. 
per  ton. 

Note  should  be  made  of  the  fact  that  successful  experiments 
with  cyanide  on  silver  ore  had  been  made  earlier  at  the  mines 
in  Sinaloa,  but  the  results  had  not  been  heralded  because  they 
were  obtained  at  private  properties,  and  even  in  these  cases  the 
official  tests  of  the  cyanide  company  at  Mexico  City  had  discour- 
aged hope.  The  trouble  was  due  to  the  use  of  too  weak  a  solution — 
a  swing  of  the  pendulum  in  cyanide  practice,  for  in  its  early  days 
the  main  fault  was  the  employment  of  a  needlessly  strong  solution. 
Another  factor,  that  prevented  success  with  these  silver  ores, 
was  the  insufficient  time  given  for  chemical  action.  The  element 


METALLURGICAL  DEVELOPMENT.  261 

of  time  is  especially  important  in  the  case  of  concentrate — iron 
pyrite  carrying  gold  free  and  silver  as  argentite;  the  millman  can 
afford  to  give  the  time  required  because  of  the  small  quantity  of 
this  product  and  its  richness. 


TREATMENT  OF  MATTE  FROM  THE  CYANIDE 

MILL 

BY  A.  E.  DRUCKER 

(May  18,  1907) 

It  may  be  of  interest  to  some  to  know  of  a  quick  and  com- 
plete way  in  which  to  extract  the  metals  from  a  rich  matte  as 
obtained  at  a  cyanide  clean-up.  It  often  happens  that  the  yield 
from  this  source  adds  considerably  to  the  month's  bullion. 

Sulphur,  the  matte-forming  element,  comes  from  the  zinc 
sulphate  (ZnSO4)  remaining  with  the  precipitate  after  acid  treat- 
ment. The  amount  of  ZnSO4  present  will  depend,  of  course, 
upon  the  number  of  water- washes  used  in  the  final  acid  treatment. 
The  more  the  precipitate  is  washed,  the  less  will  be  the  matte 
formed  on  a  gold  button.  I  believe  that  in  our  case  (treatment 
of  concentrate)  it  is  possible  at  times  for  extermely  fine  material 
to  escape  from  the  filters,  to  be  carried  in  suspension  to  the  zinc- 
boxes  where  it  is  bound  to  remain  with  the  other  precipitate. 
The  amount,  however,  is  exceedingly  small.  If  such  be  the  case 
after  treatment  with  acid,  ferrous  sulphate  (FeSO4)  will  be  con- 
tained in  solution,  while  free  sulphur  separates  out  with  the  pre- 
cipitate according  to  the  reaction: 

FeS2  +  H2SO4  =  FeSO4  +  H2S  +  S. 

There  is  a  possibility  then,  unless  a  complete  roast  is  given 
to  the  acid-treated  precipitate,  of  sulphur  being  present  as  a  matte- 
forming  material  upon  melting  the  final  precipitate.  The  amount 
of  sulphur  obtained  from  this  source  to  form  matte  will  in  all 
probability  be  slight.  Experiments  now  point  to  the  fact  that  the 
amount  of  matte  obtained  on  a  gold  button  depends  principally 
upon  two  things,  namely,  the  completeness  of  the  final  water- 
washes  after  acid  treatment  and  the  extent  to  which  the  final 
roast  has  been  carried  (whether  merely  a  drying  of  the  precipitate 
or  a  complete  roast). 

The  matte  that  I  am  treating  contains  zinc,  lead,  iron,  gold, 
and  silver.  When  using  the  zinc-lead  couple  for  precipitation, 
the  presence  of  lead  in  the  matte,  if  the  gold  slime  is  acid-treated 
and  then  smelted  in  a  graphite  pot,  is  practically  inevitable. 


TREATMENT  OF  MATTE. 


263 


Lead  in  the  matte  may  also  be  due  partly  to  the  dissolving  (by  the 
cyanide  solution)  of  lead  salts  from  oxidized  concentrate  fol- 
lowed by  the  precipitation  of  lead  on  the  zinc.  It  may  originate 
from  the  lead  acetate  used  in  some  solutions.  There  are  two 
sources  by  which  iron  may  enter  the  matte,  either  by  iron  pyrite  col- 
lecting in  the  zinc-boxes  and  finally  appearing  in  the  acid-treated 
precipitate  as  FeSO4,  or  by  some  iron  scale  gathered  from  the 


Fig.  33.     Oriental  Consolidated  Mill.     Korea. 

roasting-pan  with  the  gold  precipitate.  Zinc  seems  to  enter  the 
matte  in  considerable  amount,  especially  when  the  acid-treated 
slime  contains  some  undissolved  zinc  or  has  been  only  partly 
roasted,  so  as  to  contain  zinc  sulphate. 

I  believe  that  a  small  amount  of  matte  on  a  button  is  desirable, 
for  the  slag  above  will,  as  a  general  rule,  assay  less  in  silver,  especi- 
ally when  the  matte  contains  lead.  No  nitre  is  used  by  us  to  keep 
down  the  matte  upon  fusion  of  the  slime  in  crucibles.  Its  dam- 


264  RECENT  CYANIDE  PRACTICE. 

age  to  the  pots  amounts  to  more  than  the  cost  of  treatment  of 
the  additional  matte.  Previously  to  using  my  present  method 
of  reduction,  we  certainly  did  not  welcome  the  presence  of  any 
considerable  amount  of  matte  at  a  clean-up,  since  the  old  method 
of  treating  small  quantities  with  nitre  or  scrap  iron  was  slow  and 
incomplete.  It  is  not  safe  to  allow  any  amount  of  this  rich  matte 
to  accumulate  (it  assays  about  $20  per  Ib.)  and  for  that  reason 
the  best  plan  is  to  treat  it  immediately  at  the  end  of  the  clean-up, 
melting  the  bullion  with  the  gold  buttons  into  bars. 

Potassium  cyanide  acts  as  a  powerful  reducing  and  desul- 
phurizing flux,  and  for  this  reason  it  was  used  for  decomposing 
the  matte.  Our  particular  matte  is  unusually  high-grade,  assay- 
ing as  much  as  $45,000  per  ton.  It  contains  zinc,  lead,  and  iron 
as  sulphides,  besides  the  precious  metals.  At  the  monthly  clean-up 
about  800  Ib.  precipitate  is  obtained,  producing  nearly  3,000  oz. 
bullion,  and  from  the  treatment  of  this  we  obtain  from  30  to  40 
Ib.  matte.  The  amount  varies  from  month  to  month.  The  method 
of  treatment  for  the  matte  is  as  follows : 

The  matte,  borax,  and  cyanide  are  put  separately  through 
a  small  rock-breaker  and  crushed  fine.  Borax  and  cyanide  are 
used  as  fluxes  and  are  put  with  the  matte  into  three  No. :  60  graphite 
pots  in  the  following  proportions  and  order:  There  are  alternate 
layers  of  borax,  matte,  and  cyanide  throughout,  until  the  pot 
is  full,  and  finally  covered  with  borax.  The  crucibles  are  now 
put  into  the  furnace  and  a  white  heat  maintained  for  two  or  three 
hours.  As  a  rule,  it  takes  a  little  over  two  hours  with  a  good 
hot  furnace.  It  can  be  seen  when  the  action  is  complete,  for  the 
charge  will  subside  and  the  bubbling  cease.  The  action  and  burn- 
ing of  the  sulphur  will  be  violent  at  the  end  of  the  first  hour. 
Also  the  slag  will  become  quite  thick  when  the  action  is  complete, 
being  removed  with  a  skimmer;  this  is  necessary  before  pouring 
the  contents  of  the  crucible  into  a  conical  mold.  If  an  excess 
of  cyanide  be  used,  it  will  be  found  just  above  the  gold  button 
and  can  be  broken  off  by  a  blow  with  a  hammer.  The  matte  will 
now  be  entirely  decomposed,  leaving  only  a  light  porous  slag  and 
the  gold  button. 

This  method  shows  an  extraction  of  85  to  94%  of  the  total 
value  of  the  original  matte,  depending  upon  the  richness  of  the 
material  treated. 


CYANIDE  PRACTICE  AT  COP  ALA 

(June  8,  1907) 

The  Editor: 

Sir — In  regard  to  saving  cyanide  in  the  treatment  of  gold 
and  silver  ore,  we  have  been  enabled  by  a  simple  method  to  reduce 
our  cyanide  consumption  from  4.5  to  1.5  Ib.  per  ton  of  ore  treated, 
and  the  results  are  so  interesting  that  I  herewith  tender  them  for 
publication. 

When  we  first  commenced  treatment  in  October,  1905,  our 
protective  alkalinity  in  the  working  solutions  was  carried  at  0.04% 
(in  terms  of  caustic  soda),  and  the  cyanide  consumption  varied 
from  4.3  to  4.5  Ib.  per  ton  of  ore. 

The  ore  is  valuable  for  its  silver,  which  occurs  as  a  sulphide, 
and  carries  from  12  to  20  oz.  of  this  metal  per  ton,  together 
with  a  small  quantity  of  gold.  We  find  that  5.2  Ib.  of  lime  per 
ton  is  sufficient  to  keep  the  alkalinity  at  0.04%.  Our  extraction 
has  been  good,  averaging  93%  of  both  gold  and  silver,  and,  accept- 
ing the  fact  that  a  certain  amount  of  cyanide  will  of  necessity  be 
constantly  tied  up  as  a  double  cyanide  of  zinc  and  sodium  (using 
sodium  cyanide),  we  have  not  considered  the  amount  abnormal, 
though  the  advisability  had  been  discussed  of  installing  electro- 
lytic precipitation  to  obviate  this  loss  of  potential  free  cyanide. 
However,  in  reading  over  'The  Cyaniding  of  Gold  and  Silver  Ores,' 
by  Julian  and  Smart,  I  noted  what  was  said  (page  99)  in  regard  to 
the  decomposition  of  the  double  cyanide  (Na2ZnCy4)  by  an  increase 
in  the  free  alkali.  W.  R.  Feldtman  is  there  quoted  as  saying: 
"The  addition  of  alkali  to  working  cyanide  solutions  which  have 
become  somewhat  weak  in  alkali,  brings  up  the  strength  by 
regenerating,  that  is,  decomposing,  the  zinc  cyanide,  so  that  as  a 
matter  of  fact,  when  the  solutions  are  pretty  strongly  alkaline  they 
contain  no  zinc  as  cyanide,  but  only  the  hydrate  dissolved  in 
alkali." 

With  the  object  of  ascertaining  what  results  could  be  obtained 
by  increasing  the  alkalinity,  I  commenced  adding  lime,  and  kept 
gradually  increasing  the  same  until  the  solutions  tested  0.2% 
alkalinity.  Our  working  solution  for  slime,  which  we  carry  at 
0.125%  KCy,  at  once  began  to  gain  in  strength,  and  kept  growing 


266  RECENT  CYANIDE  PRACTICE. 

gradually  stronger  until  it  showed  0.3%  KCy;  the  alkalinity  was 
then  allowed  to  fall  to  0.09%,  when  cyanide-  strength  also  fell. 
After  many  experiments  with  various  strengths,  I  found  0.135% 
to  be  the  least  alkalinity  with  which  I  could  regenerate,  and  con- 
sequently I  have  kept  the  alkali  at  that  strength  ever  since. 

As  a  result  of  this  regeneration,  our  cyanide  consumption  has 
not  exceeded  1.5  Ib.  per  ton  treated  for  more  than  five  months; 
as  a  matter  of  fact,  no  cyanide  was  added  to  the  slime-treatment 
solutions  for  nearly  13  weeks,  and  the  amount  used  to  bring  the 
leaching-plant  solutions  up  to  strength  was  small;  this  of  course 
was  due  to  the  large  excess  of  zinc  cyanide  then  existing  in  the 
system. 

In  regard  to  the  testing  for  alkali,  we  first  determine  the  free 
cyanide  by  titrating  with  standard  silver  nitrate  solution  to  the 
first  faint  opalescence,  without  the  use  of  the  potassium  iodide 
indicator;  we  then  add  a  few  drops  more  of  the  silver  nitrate  to 
make  the  opalescence  well  defined,  and  titrate  with  N/5  oxalic 
acid  solution  using  phenolphthalein  as  indicator.  This  is  the 
method  recommended  by  J.  E.  Clennell,  and  as  it  has  been  found 
to  check  very  closely  with  L.  M.  Green's  ferrocyanide  method,  and 
also  with  that  of  Gerard  Williams  published  in  the  Journal  of  the 
Chemical,  Metallurgical  &  Mining  Society  of  South  Africa,  it  has 
been  adopted  by  preference  on  account  of  its  simplicity. 

Finally,  I  would  say  that  up  to  date  there  is  no  indication  of 
increase  in  our  cyanide  consumption,  and  as  this  work  has  been 
going  on  for  the  past  five  months  I  have  come  to  the  conclusion 
that  the  regeneration  has  assumed  constant  proportion. 

L.  McN.  B.  BULLOCK. 

Copala,  Sinaloa,  Mexico,  May  4. 


ASSAY  OF  CYANIDE  SOLUTIONS 

(June  8,  1907) 

The  Editor: 

Sir — Having  noticed  the  schemes  for  the  'Assay  of  Cyanide 
Solutions'  in  the  PRESS  of  March  30,  by  Mr.  Gendar,  and  of  May  4, 
by  Mr.  Muir,  I  wish  to  call  attention  to  the  following  well  known 
method,  which  I  have  found  quick  and  accurate. 

To  a  convenient  quantity  of  KCN  (working  solution)  add  an 
excess  of  weak  copper  sulphate  solution.  Acidify  with  dilute 
sulphuric  acid.  Filter  the  precipitate,  which  is  white  (or  light- 
bluish  green)  and  flocculent,  and  which  contains  all  the  gold  and 
silver.  Wash  the  precipitate  twice  with  hot  water;  dry  filter- 
paper  and  contents  by  placing  them  in  a  crucible  and  heating  in 
a  muffle;  flux  filter-paper  and  precipitate,  fuse,  cupel,  part,  and 
weigh. 

To  solutions  weak  in  KCN  add  a  small  piece  of  KCN  salt, 
in  order  to  give  a  good  precipitate  of  copper  cyanide. 

AUGUSTUS  MACDONALD. 

Zacatecas,  Mexico,  May  17. 


(June  8,  1907.) 

Some  time  ago  Messrs.  G.  A.  and  H.  S.  Denny  announced, 
with  a  great  flare  of  trumpets,  the  triumph  of  their  metallurgical 
innovation.  Several  of  the  mines  under  their  technical  control 
spent  thousands  of  pounds  to  install  the  process  of  circulating 
cyanide  solutions,  advocated  by  the  Denny  brothers.  The  fol- 
lowing paragraph  from  a  speech  delivered  at  the  annual  meeting 
of  the  New  Goch  mine,  by  Mr.  George  Albu,  the  chairman,  is  rather 
disconcerting  to  the  'new  metallurgy:'  "In  addition  to  other 
drawbacks,  we  have  experienced  considerable  trouble  with  our 
new  metallurgical  plant.  Whatever  theoretical  merits  the  system 
of  circulating  cyanide  solutions  may  possess,  the  fact  remains 
that  the  one  check  depended  upon  to  ascertain  the  average 
value  of  the  ore  going  into  the  mill,  namely,  the  screen-assay,  is 
effectually  destroyed.  Our  managers  and  technical  advisers  have 
endeavored  to  overcome  this  difficulty,  but  apparently  without 
any  great  success,  and  consequently  we  have  been  frequently  dis- 


268  RECENT  CYANIDE  PRACTICE. 

appointed  at  the  end  of  the  month  in  the  quantity  of  gold  won, 
having  been  misled  by  the  unreliable  nature  of  the  screen-assays. 
I  do  not  propose  to  enter  into  technical  details,  but  the  sugges- 
tion is  now  under  consideration  to  abandon  the  use  of  circulating 
cyanide  solutions  and  revert  to  what  is  known  as  the  decantation 
process,  supplemented  by  the  filter-process." 

Common  caution  should  have  prevented  the  introduction  of 
the  'new  metallurgy'  on  more  than  one  mine,  until  it  was  proved 
an  unqualified  success.  Because  a  scheme  works  well  for  a  few 
weeks  it  is  not  safe  to  pronounce  it  a  success.  An  actual  working 
test  of  a  year  or  so  is  necessary  when  such  a  proposition  as  the  new 
metallurgy  is  suggested.  It  is  fortunate  for  the  rest  of  the  Rand 
that  conservative  councils  prevailed,  and  that  the  mines  of  other 
groups  did  not  take  up  the  metallurgical  schemes  so  persistently 
promulgated  by  the  Messrs.  Denny. 


THE  FILTRATION  OF  SLIME  BY  THE  BUTTERS 

METHOD 

BY  E.  M.  HAMILTON 

(June  22  and  29,   1907) 

As  the  Butters  patent  filter  has  now  been  in  operation  for 
nearly  three  years,  it  may  fairly  be  considered  a  practical  success, 
and  the  aim  of  the  present  paper  is  to  give  a  detailed  description 
of  its  inception,  construction,  and  method  of  working,  in  the  hope 
that  it  ma)'  prove  of  general  interest  to  the  mining  community. 

The  need  of  a  filter  of  some  sort  was  first  forcibly  presented  to 
the  minds  of  Charles  Butters  and  his  associates  at  their  works  in 
Virginia  City,  Nevada.  The  tailing  being  cyanided  there  was 
originally  derived  from  the  Comstock  mills,  but  it  has  been  treated 
and  re-treated  several  times  by  the  pan-amalgamation  process, 
and  as  it  stands  today  in  the  dams  it  contains  about  75  per  cent 
of  material  that  is  unleachable,  and  which  may,  therefore,  be 
designated  as  'slime.'  And  this  slime  is  of  an  exceptional  char- 
acter. In  addition  to  the  difficulties  connected  with  solution  of 
the  gold  and  silver  contents,  which  it  is  not  proposed  to  touch 
upon  in  this  paper,  the  mechanical  condition  of  it  is  such  that  it 
gives  trouble  in  settlement  for  decant ation.  The  clarification  pro- 
duced by  a  coagulent  such  as  lime  is  perfect,  but  the  subsidence 
is  so  slow  that  the  amount  of  solution  recoverable  in  this  way  is 
not  enough  to  make  the  decantation  process  a  practical  success. 
A  70-ton  charge,  with  a  four  to  one  dilution,  will  in  24  hours  not 
settle  to  less  than  three  parts  by  weight  of  solution  to  one  of  slime, 
and  the  thickest  pulp  obtainable  by  two  or  three  days'  settlement  in 
the  deep  vats  will  still  contain  about  two  of  solution  to  one  of  slime. 

A  curious  point  about  it  is  that  even  after  being  washed  in 
many  changes  of  clean  water  to  remove  all  soluble  salts,  it  will 
still  settle  in  a  medium  of  distilled  water  more  rapidly  and  com- 
pactly than  in  any  solution  hitherto  tried,  whether  acid  or  alkaline. 
When  lime,  however,  is  added  to  the  pulp  the  mixture  seems  to 
coagulate  into  a  gelatinous  curd,  and  the  slime  loses  to  a  large 
extent  its  power  to  separate  out  by  gravity. 

Here  are  displayed  in  a  marked  manner  the  phenomena  men- 
tioned by  Julian  and  Smart  in  'Cyaniding  Gold  and  Silver  Ores/ 


270  RECENT  CYANIDE  PRACTICE. 

namely,  that  coagulation  is  not  necessarily  accompanied  by  good 
settlement,  and  that  under  certain  circumstances  excessive  coagu- 
lation is  positively  injurious.  In  one  instance  a  sample  of  slime, 
from  which  most  of  the  fine  silica  had  been  removed  by  careful 
separation,  was  diluted  in  the  proportion  of  four  of  water  to  one 
of  slime,  and  sufficient  lime  added  to  neutralize  the  charge  and  leave 
about  0.05  per  cent  of  free  alkali  in  solution;  this  pulp  was  then 
placed  in  a  graduated  litre  cylinder,  where  its  level  stood  at  the 
875-c.c.  mark.  At  the  end  of  24  hours  the  solids  had  not  sub- 
sided through  more  than  four  divisions  of  the  scale,  a  distance 
equivalent  to  40  c.c.  of  solution. 

Another  fact  pointed  out  by  the  same  authors,  in  regard  to  the 
quality  of  the  settled  slime  produced  by  different  electrolytes,  is 
also  exemplified  on  this  material,  for  the  use  of  caustic  potash  in- 
stead of  lime  produces  a  curd  of  much  finer  grain,  which  settles 
better  in  every  way,  and  finally  yields  a  good  clarification  also, 
though  the  latter  proceeds  more  slowly  than  the  subsidence  of 
the  well-marked  line  of  solids,  and  the  solution  has  not  the  bril- 
liancy of  that  settled  with  lime.  Thus,  if  the  filter  method  had 
not  been  adopted  it  is  probable  that  caustic  soda  or  potash  would 
have  been  more  useful  than  lime  as  a  protective  alkali. 

In  regard  to  the  settlement  in  distilled  water,  if  it  be  true  that 
some  degree  of  coagulation  is  a  necessary  precursor  to  settlement 
and  clarification,  then  the  slime  being  treated  must  either  possess 
some  inherent  power  to  coagulate,  or  else,  in  spite  of  thorough 
washing,  must  develop  sufficient  soluble  material  by  standing  in 
water  to  form  an  electrolyte  suitable  for  this  purpose. 

It  may  be  interesting  here  to  give  a  few  results,  out  of  a  num- 
ber of  determinations,  on  the  rate  of  settlement  of  this  slime. 
These  tests  were  made  on  an  average  sample  such  as  is  usually 
treated  in  the  vats.  The  accompanying  diagram  will  illustrate. 
(See  Fig.  34.)  The  arrow-heads  denote  the  defined  surface  lines  of 
subsiding  solids;  the  percentage  figures  on  the  right-hand  side  of 
each  cylinder  represent  the  percentage  of  moisture  still  held  by 
the  settled  slime  at  that  point.  The  following  notes  will  explain: 

CYLINDER  NO.  1.— This  sample  of  slime  was  washed  in  10 
changes  of  clear  service-water,  the  operation  extending  over  sev- 
eral days,  and  finishing  with  distilled  water.  When  this  last  wash 
had  been  settled  and  decanted,  distilled  water  was  used  to  bring 
up  the  dilution  to  4  to  1.  The  line  of  subsidence  was  well  defined 


FILTRATION  OF  SLIME. 


271 


from  the  start,  but  the  liquor  retained  a  faint  opal  tint,  which 
did  not  disappear  throughout  the  test. 

CYLINDERS  NO.  2  and  3.— These  were  both  neutralized 
with_their  respective  alkalis  for  two  days  before  beginning  the  test, 
so  as.to  insure  having  an  approximately  constant  strength  of  free 
alkali  in  solution  during  the  time  of  settlement ;  in  the  case  of 
the  lime  this  strength  was  0.035  per  cent  alkalinity,  and  in  that 
of  the  caustic  potash  0.08  per  cent,  both  in  terms  of  caustic  potash. 


Cylinder  I. 

Distilled 


Cvli-nder- II.. 
Li-me. 

.035^  Solytio-n. 


Caustic  potash. 
.08/9  Solutio-n. 


CYii*dCYlV                                       cvli-nder  V 

£ul 
''.    '\ 

p  h  U  T  i  C 

acid. 

'    '1 

A  1  u  -m 

cc 

cc 

1000 

~  1000 

—SO 

3jfcvt-£  of  -&-o  xtx^d.  —  > 

800 

-80%  

—  900 

—  8 

—  5"0 

^-s* 

C~fvo-u/r3.  » 

i  —  yoo 

^ 

-TOO 

^-600 

600 

/Z,  "n^nx-r^    ~-         i 

—  SO 

i      *TA^                          6  "Ka-u/r-d    .  i 

CQ 

t      Y£ 

2.4  £     —  <            ! 

500 

(  —  u9^L                            '^."^ft-u.-r'j    -            • 

500 

L. 

£*^^ 

—  SO 

—  SO 

\     g. 

48  K*t^rtf.               > 

=  400 

1     G3^                      48<»u^-j  i 

g  400 

(  g/ 

—  ^0 

300 

300 

r—SO 

—  SO 

too 

200 

—  50 

—so 

100 

100 

r-^ 

—  ^                        ,  

—so 

<  

Fig.  34. 


272  RECENT  CYANIDE  PRACTICE. 

Similar  tests,  made  with  considerably  larger  amounts  of  free 
alkali  in  solution,  showed  slightly  inferior  results  in  the  case  of 
lime,  but  a  tendency  to  closer  settlement  with  caustic  potash.  In 
the  case  of  cylinder  No.  2,  the  lime  left  a  sparkle  and  limpidity  of 
the  supernatant  solution  lacking  in  that  settled  with  caustic  pot- 
ash, though  the  latter  might  be  said  to  be  perfectly  clear  unless 
compared  with  No.  2,  when  a  difference  would  become  apparent. 

CYLINDER  NO.  4. — In  this  test  the  same  amount  of  slime 
was  taken  as  before,  and  the  same  proportion  of  water  added. 
Sufficient  pure  sulphuric  acid  was  then  mixed  with  it  to  leave  a 
little  free  acid  in  excess  after  dissolving  all  it  would  of  the  soluble 
material.  In  this  medium  the  slime  settled  better. than  in  the 
lime  solution,  but  the  liquid  remained  slightly  opalescent. 

CYLINDER  NO.  5.— To  this  five  grams  of  alum  were  added 
and  allowed  to  dissolve,  giving  a  result  nearly  as  good  as  that 
obtained  with  caustic  potash,  and  a  solution  of  about  the  same 
degree  of  clearness,  that  is,  clean,  but  lacking  the  absolute  purity 
of  the  lime  solution. 

The  experiments  here  given  will  be  sufficient  to  indicate  the 
nature  of  the  material  to  be  treated,  which  has  a  bearing  on  the 
results  obtained  by  the  use  of  the  filter. 

After  experimenting  with  several  forms  of  vacuum-filter  units, 
both  cylindrical  and  rectangular,  the  system  hereinafter  described 
was  finally  evolved,  and  very  few  changes  have  been  made  in  it 
since  the  first  appliance  was  installed  on  a  working  scale  in  the 
Virginia  City  plant. 

As  at  present  constructed  the  filter-leaf  is  made  on  a  frame, 
the  upper  side  of  which  is  formed  on  a  bar  of  wood,  If  in.  thick 
and  5J  in.  wide,  placed  on  edge,  and  10  ft.  in  length,  or  sufficiently 
long  for  its  ends  to  rest  on  top  of  the  containing  box  from  side 
to  side.  (See  Fig.  35.)  The  remaining  three  sides  of  the  frame 
are  made  of  J-in.  pipe,  one  extremity  of  which  is  flattened,  turned 
at  a  right  angle,  and  firmly  bolted  to  the  under  side  of  the  wooden 
bar,  while  the  other  extremity  projects  through  the  other  end  of 
the  same  bar,  in  order  to  receive  its  connection  with  the  vacuum- 
chamber,  being  tightly  clamped  to  the  wood  at  the  point  where 
it  passes  through.  The  upper  face  of  that  portion  of  the  pipe 
forming  the  bottom  of  the  frame  is  pierced  with  5/io-in.  holes  at 
intervals  of  four  inches  for  its  whole  length,  and  through  these 
the  solution  passes  off  from  the  filter  into  the  receiver. 


274  RECENT  CYANIDE  PRACTICE. 

The  filtering  medium  consists,  first,  of  a  piece  of  cocoa  mat, 
of  such  a  size  as  exactly  to  fill  the  space  formed  by  the  frame 
described  above.  On  either  side  of  this  is  placed  a  sheet  of  16-oz. 
canvas,  large  enough  to  overlap  the  frame.  These  three  thick- 
nesses of  material  are  then  sewed  together  by  machine  with  par- 
allel rows  of  stitching  four  inches  apart,*  and  perpendicular  to 
the  sustaining  wooden  bar.  Next,  the  filtering  medium  so  formed 
is  fitted  in  the  frame,  the  overlapping  canvas  edges  being  stitched 
round  the  outside  of  the  piping,  and  the  upper  edge  fastened 
to  the  wooden  bar  by  being  sunk  in  the  groove  shown  in  the  draw- 
ing and  a  lath  driven  in  over  it,  wedging  it  firmly  in  position. 
This  lath  is  also  made  to  fulfill  another  function ;  instead  of  being  of 
such  a  thickness  as  to  be  driven  flush  with  the  surface  of  the  wood, 
it  is  made  to  project  outward  for  a  distance  of  about  half  an  inch, 
and  the  under  side  of  this  projection  is  grooved  or  weathered  so 
as  to  deflect  the  drippings  of  solution  that  run  down  off  the  bar 
when  the  pulp  is  withdrawn,  and  prevent  them  from  trickling 
over  the  surface  of  the  newly-formed  cake.  This  action  was 
found  to  cut  channels  in  the  surface  of  the  slime,  and  form  the 
starting  points  of  cracks.  A  point  to  be  noticed  in  the  section 
(of  the  head  of  the  frame)  is  the  shoulder,  formed  by  the  lower 
angle  of  the  wooden  top,  over  which  the  canvas  has  to  be  strained 
before  reaching  its  attachment.  The  lack  of  support  at  this  point 
between  the  canvas  and  the  cocoa  mat  was  found  to  cause  a 
tendency  to  start  cracks  in  the  cake,  and  to  avoid  this  the  ma- 
terial is  rendered  impervious  with  P.  &  B.  paint  down  to  the  line 
at  which  it  comes  in  contact  with  the  mat,  which  is  about  1J 
in.  below  the  lower  extremity  of  the  wooden  support.  At  this 
point  there  is  a  horizontal  line  of  stitching  holding  the  three 
thicknesses  of  material  together.  The  paint  is  also  applied  all 
round  the  frame  of  pipe  in  a  border  about  an  inch  wide,  for  the 
same  reason,  and  this  has  proved  a  simple  way  of  meeting  the 
difficulty,  and  giving  the  cake  a  perfectly  plane  surface  on  which 
to  build  itself  up. 

After  everything  has  been  done,  six  or  seven  strips  of  wood 
are  placed  vertically  on  each  side  of  the  leaf,  thus  dividing  it 
into  a  number  of  panels  of  equal  size;  these  reach  from  top  to 
bottom  of  the  frame  and  are  screwed  together  through  the  filtering 
material.  They  act  as  braces  to  stiffen  the  frame  and  also  to 


*The  latest  plan  is  to  have  these  rows  of  stitching  only  one  inch  apart;    this  gives  greater 
strength  and  rigidity. 


U--03 


I 


CO 
CO 

bb 

a 


276  RECENT  CYANIDE  PRACTICE. 

hold  the  canvas  vertical  and  prevent  it  from  sagging  out  to  one 
side  or  th£  other. 

For  localities  where  water  is  scarce,  and  generally  where  it  is 
desirable  to  send  out  a  comparatively  dry  cake,  the  frame  of  the 
leaf  is  now  modified  to  admit  of  throwing  off  the  cake  without 
previously  submerging  it  in  water  as  is  done  at  Virginia  City. 
The  frame  of  pipe  in  this  case  is  made  to  extend  round  all  four 
sides  instead  of  only  three;  the  extremities  pass  through  the 
wooden  bar  at  each  end  instead  of  only  at  one  end  of  it,  and  the 
pipe  at  the  upper  side  of  the  frame  is  perforated  like  the  lower 
one.  B^  this  arrangement,  water  can  be  injected  into  the  leaf 
along  the  top  through  one  of  the  projecting  extensions  of  the 
pipe,  and  simultaneously  compressed  air  can  be  admitted  through 
the  other  pipe  into  the  lower  part  of  the  frame.  This  has  been 
found  to  make  a  perfect  discharge  of  the  cake  into  the  empty 
box,  whereas  water  alone  could  not  be  made  to  give  a  proper  dis- 
charge unless  the  cakes  were  submerged. 

Compressed  air,  alone,  can  be  used  for  a  dry  discharge,  but  it 
is  not  as  satisfactory  as  the  combination  of  water  and  air  simul- 
taneously. (See  Fig.  36.) 

At  Virginia  City  the  containing  box  is  an  electrolytic  precipi- 
tation box  which  was  not  needed  for  its  special  purpose  and  was 
adapted  to  the  use  of  the  new  filter,  being  allowed  to  remain  in 
its  original  position.  It  was  formerly  divided  into  12  compart- 
ments, each  having  a  hopper-bottom;  the  partitions  were  removed, 
and  with  them  two  of  the  sides  of  each  hopper,  so  that  the  whole 
space  was  vacant  from  end  to  end,  and  after  the  heavy  top  rails 
had  been  removed  the  result  was  a  box  31  ft.  8  in.  long  and  9  ft. 
11  in.  wide,  the  sides  being  vertical  for  a  depth  of  five  feet  and 
then  meeting  the  V-shaped  bottom. 

In  place  of  the  top  rails,  boards  5f  in.  wide  and  1  in.  thick  were 
placed  horizontally  on  the  top  edges  of  the  box,  and  on  the  outer 
edge  of  these  were  fixed  vertical  boards  12  in.  high  and  If  in. 
thick,  all  being  well  bolted  together  and  to  the  box,  the  result  was 
to  raise  the  sides  10  in.  higher  than  they  were  when  used  for  pre- 
cipitation. The  two  shelves  thus  formed  along  the  sides  of  the  box 
serve  to  carry  the  ends  of  the  filter-leaf  bars  and  allow  the  leaves 
to  hang  free  inside  the  box  (Fig.  37.)  On  one  side  of  the  sloping 
bottom  and  extending  down  to  its  lowest  point  are  four  discharge- 
doors,  each  giving  an  aperture  of  12  in.  square;  the  doors  are 


278  RECENT  CYANIDE  PRACTICE. 

hinged  on  their  lower  sides,  and  seat  on  a  rubber  insertion  led 
into  the  iron  frame;  they  are  closed  by  hand,  and  then  held  in 
position  by  a  lever.  To  discharge  the  contents  of  the  box  it  is 
only  necessary  to  shift  the  lever,  and  the  door  drops  open  by 
its  own  weight.  At  each  end  of  the  box  is  another  door  10  in. 
square,  through  which  the  nozzle  of  a  hose  is  manipulated  for 
flushing  out  any  hard  slime  that  may  remain  behind  in  the  bottom. 

When  designing  a  containing-box  for  the  special  purpose  of 
the  filter,  the  lines  of  the  original  box  are  departed  from  as  regards 
the  shape  of  the  bottom,  which  is  then  composed  of  one  or  more 
complete  hoppers  of  about  60°  for  the  better  discharge  of  the 
cake,  and  the  door  of  each  hopper  is  placed  at  its  apex  and  may 
be  a  12-in.  quick-opening  valve  or  any  other  suitable  device. 
With  such  an  arrangement  the  residue  gravitates  out  without 
the  aid  of  any  washing  with  hoses. 

At  Virginia  City  the  exhaust -pump  is  a  converted  compressor, 
which  happened  to  be  on  hand.  It  was  made  by  the  Rix  Com- 
pressed Air  &  Drill  Co.  of  San  Francisco,  and  is  described  in 
their  catalogue  as  a  "vertical  duplex  blowing  engine."  It  has 
two  cylinders  14  in.  by  8  in.  and  is  belt-driven,  the  crank-shaft 
making  120  rev.  per  min.  Only  one  cylinder  is  used  for  the  pur- 
pose of  the  filter,  the  other  being  connected  with  a  separate  drum 
and  used  to  form  a  vacuum  for  drying  out  the  final  washes  from 
the  sand-leaching  vats. 

The  vacuum-drum  is  of  riveted  boiler-plate,  and  is  3  ft.  8  in. 
diameter,  13  ft.  4  in.  long,  standing  upright  on  its  end.  The 
pipe  from  the  vacuum-pump  enters  at  the  top ,  while  the  pipe  con- 
necting with  the  filters  enters  4  ft.  from  the  bottom.  At  or  near 
the  bottom  a  drain-pipe  enters,  for  removing  the  solution  as  it 
is  drawn  in  from  the  filter-leaves.  This  pipe  passes  down  into  a 
small  sump  22  ft.  below,  so  that  the  solution  will  drain  by  gravity 
and  keep  the  chamber  empty.  The  level  of  the  solution  in  the 
sump  is,  of  course,  always  kept  above  the  discharge  to  prevent 
the  entrance  of  air  into  the  drum.  The  average  barometric  pres- 
sure at  the  level  of  the  works  is  24.5  and  the  average  vacuum 
maintained  is  22.5  in.,  which  is  indicated  by  a  column  of  mercury 
connected  with  the  drum.  As  the  small  receiving-sump  fills  with 
solution,  it  is  periodically  pumped  into  a  storage- vat,  from  which 
it  passes  to  the  precipitation-boxes. 

Instead  of  the  dry  vacuum-pump  and  gravity-drainage,  a  'wet* 


FILTRATION  OF  SLIME  279 

vacuum-pump  may  be  used,  which  would  obviate  the  necessity 
for  placing  a  solution-sump  20  to  30  ft.  below  the  filter-level,  in 
cases  where  such  an  arrangement  might  be  difficult  or  undesirable. 

The  filter-leaves  are  placed  in  the  containing-box  at  a  distance 
from  each  other  of  about  four  inches  from  centre  to  centre,  and 
are  then  ready  to  be  connected  with  the  vacuum-drum.  One 
space  is  usually  left  vacant  midway  along  the  box  to  allow  access 
to  the  surface  of  the  leaf  for  purposes  of  measuring  the  formation 
of  the  cake,  and  also  of  admitting  an  electric  light  to  observe  its 
condition  after  the  charge  of  pulp  has  been  withdrawn.  Blocks 
of  wood  are  fastened  on  the  shelves  that  carry  the  filter-leaf  bars 
to  act  as  spacers  between  the  leaves,  and  it  is  generally  found  ad- 
visable also  to  use  a  line  of  blocks  or  iron  clamps  down  the  centre 
of  the  row  of  frames  to  prevent  the  bars  from  sagging  horizontally 
toward  one  another  under  the  weight  of  the  cake.  The  ends 
of  the  bars,  too,  need  to  be  held  down  in  their  places  by 
wooden  buttons,  to  prevent  them  from  floating  up  by  the  action 
of  the  bouyancy  of  the  thick  pulp. 

A  4-in.  pipe  runs  the  whole  length  of  one  side  of  the  containing- 
box,  and  has  a  number  of  small  horizontal  holes  bored  in  it,  one 
exactly  over  each  filter-leaf;  into  each  hole  is  screwed  a  J-in. 
nipple  and  plug-cock,  on  the  further  side  of  which  is  a  union 
into  which  screws  the  small  end  of  a  reducing  ell;  the  large  end 
of  the  small  ell  enters  a  short  length  of  rubber  hose,  which  con- 
nects with  the  projecting  end  of  pipe  from  the  filter-frame  (Fig. 
35).  Thus,  by  unscrewing  the  union  any  individual  leaf  may  be 
disconnected  and  removed  from  the  box  in  a  few  minutes. 

At  each  end  of  the  4-in.  pipe  is  a  quick-opening  valve ;  one  is 
connected  with  the  vacuum-drum,  and  by  opening  it  the  suction 
is  applied  to  the  filters.  The  other  unites  with  a  low-pressure 
water-service  of  about  20  ft.  head,  and  through  it  water  is 
admitted  between  the  two  sheets  of  canvas  for  the  purpose  of 
detaching  the  residue-cake  prior  to  discharging. 

There  is  also  a  f-in.  pipe  running  all  around  the  top  of  the  box; 
this  has  holes  pierced  in  its  under  side,  and  is  connected  with  a 
small  solution-vat  above;  its  function  is  to  form  a  spray  to  wash 
down  the  sides  of  the  box  when  the  pulp  is  withdrawn,  so  as  to 
reduce  to  a  minimum  the  amount  of  slime  introduced  into  the 
solution-vat  when  the  subsequent  wash  is  thrown  back,  and  also 
to  minimize  the  loss  of  valuable  solution  in  cases  where,  as  at 


FILTRATION  OF  SLIME.  281 

Virginia  City,  a  water- wash  follows  directly  on  the  withdrawal 
of  the  surplus  pulp  and  is  discharged  with  the  residue-cakes. 

The  charge  of  slime,  after  being  treated  by  agitation  in  the 
ordinary  way,  but  not  having  received  any  subsequent  washes,  is 
allowed  to  settle  for  24  hours  in  the  treatment  vat.  When  the 
clear  solution  has  been  decanted,  the  charge  is  stirred  up  and 
run  into  a  deep  settlement-vat,  of  which  there  are  three  in  use  at 
the  present  time.  Here  it  settles,  usually  for  two  or  three  days, 
and  from  here,  after  being  decanted  as  closely  as  possible,  it  is 
taken  directly  into  the  filter. 

This  method  of  feeding  the  filter  works  well  with  the  peculiar 
slime  under  discussion,  but  for  the  more  ordinary  kinds  of  slime 
and  particularly  when  there  is  much  fine  silica  present,  it  is  found 
advisable  to  have  the  stock  pulp-vat  fitted  with  a  mechanical 
stirring-gear  to  keep  the  slime  from  settling  too  hard  for  pump- 
ing and  to  give  a  homogeneous  product  to  the  filter. 

All  transfers  in  connection  with  the  filtering  process  are  per- 
formed by  a  single  6-in.  centrifugal  pump  (see  Fig.  38)  with  valves 
and  levers  so  arranged  that  the  man  in  charge  can  carry  out  each 
operation  without  moving  from  one  spot.  From  an  examination 
of  the  pipe-connections  with  this  pump  it  will  be  seen  that  it  will 
first  draw  pulp  from  the  feed-vat  and  throw  up  through  the 
bottom  of  the  filter-box;  next,  it  will  draw  from  the  filter  and 
throw  back  through  the  bottom  of  the  feed- vat;  it  will  then 
draw  from  either  solution-vat  or  water-tank  to  fill  the  filter-box 
and  return  the  same  to  where  it  came  from. 

This  may  look  complicated  on  paper,  but  it  is  perfectly  simple 
for  the  operator,  and  a  new  hand  will  learn  the  whole  routine  in 
a  couple  of  days.  Within  easy  reach  are,  first,  the  clutch-lever 
for  starting  and  stopping  the  6-in.  pump,  and  another  for  the 
4-in.  centrifugal  used  for  emptying  the  drain  solution  sump; 
second,  two  small  winches  connected  with  wire-cord  with  the 
two  3-way  valves,  each  having  a  dial  indicator  visible  from  his 
station  to  show  exactly  the  position  of  the  valve;  third,  four  iron 
handles  projecting  through  the  floor  at  his  feet,  for  opening  and 
closing  the  straight -way  valves  of  the  system;  these  also  are 
marked,  so  that  there  may  be  no  mistake.  Within  three  feet  of 
where  he  stands  the  filter-box  is  situated,  and  close  alongside  is 
the  vacuum-drum  with  its  mercury-gauge,  and  gate  for  opening 
and  closing  the  main  vacuum-pipe;  and  30  ft.  away,  on  the  same 


282  RECENT  CYANIDE  PRACTICE. 

level,  is  the  valve  that  admits  water  to  the  leaves  for  detaching 
the  cake.  Thus,  the  only  occasions  on  which  he  need  move  more 
than  a  few  feet  away  from  his  station  are,  (1)  when  he  has  to  go 
below  to  manipulate  the  discharge-doors  of  the  box,  (2)  when  he 
has  to  change  from  one  feed- vat  to  the  next  one,  and  (3)  when  it 
is  necessary  to  oil  or  pack  one  of  the  pumps. 

METHOD  OF  PROCEDURE. — It  is  assumed  that  the  filter- 
box  is  empty  and  one  of  the  deep  settlement-vats  has  been  charged 
to  its  full  capacity  and  has  had  time  for  settlement  and  decanta- 
tion,  and  that  the  pulp  therein  is  composed  of  about  one  part  of 
slime  to  two  of  solution.  This  vat  has  six  12-in.  iron  plugs  in  the 
bottom,  connected  by  iron  rods  to  a  screw  and  wheel  attachment 
at  the  top  of  the  vat,  by  which  they  may  be  opened  or  closed  from 
above.  The  seats  of  these  valves  are  all  connected  by  tees  to  the 
6-in.  pipe  of  the  centrifugal  pump. 

In  order  to  put  the  filter  in  operation,  the  shift-man  first  opens 
up  two  of  the  plugs  in  the  deep  vat ;  he  then  returns  to  his  station 
and  opens  the  valve  between  the  vat  and  the  pump,  and  by  turn- 
ing his  winches  sets  the  3-way  valves  in  position  to  draw  from  the 
feed- vat  and  discharge  into  the  bottom  of  the  filter-box.  As  soon 
as  the  box  is  full  the  pump  is  stopped  and  the  valve  to  the 
vacuum-drum  is  opened,  putting  each  filter-leaf  in  direct  com- 
munication with  the  vacuum-pump,  which  is  now  in  action.  Very 
soon  a  subsidence  in  the  level  of  the  pulp  is  apparent,  due  to  the 
withdrawal  of  liquor  through  the  filters;  the  6-in.  pump  is  then 
started  again  to  supply  fresh  pulp  to  the  box,  and  this  is  repeated 
at  short  intervals  so  as  to  keep  the  level  of  the  pulp  always  above 
the  line  of  permeability  of  the  leaves.  The  solution,  which  is 
drawn  from  the  pulp  into  the  vacuum-drum  continually,  gravitates 
into  the  small  sump  and  is  periodically  pumped  into  the  precipita- 
tion vat,  as  before  described. 

The  thickness  of  cake  allowed  to  accumulate  on  the  leaves 
varies  from  j  to  one  inch  and  these  seem  to  be  the  economical  limits ; 
a  thickness  of  over  one  inch  necessitates  a  disproportionately 
longer  time  to  collect  and  wash  the  cake,  because  the  deposition 
becomes  slower  and  slower  with  increased  thickness,  and  the  cake 
is  more  liable  to  drop  from  its  support  when  the  pulp  is  with- 
drawn; while  if  less  than  f  in.  be  used  economy  is  again  inter- 
fered with  owing  to  the  time  needed  for  the  subsequent  operations 
being  spent  over  too  small  a  tonnage  of  material. 


FILTRATION  OF  SLIME.  283 

The  time  needed  to  accumulate  a  f-in.  cake  varies  with  the 
amount  of  moisture  held  in  the  pulp  and  with  the  quality  of  the 
.slime,  and  may  be  from  15  minutes  to  an  hour.  The  progress  of 
formation  is  estimated  from  time  to  time  by  reaching  the  hand 
below  the  level  of  the  pulp  and  passing  a  short  stick,  such  as  a 
wooden  match,  through  the  cake  and  noting  the  measurement 
between  the  canvas  surface  and  the  finger  and  thumb. 

As  soon  as  the  necessary  point  has  been  reached  no  more  pulp  is 
.supplied  to  the  box,  but  the  3- way  valves  being  reversed,  the  pump 
is  again  started,  when  the  suction  and  delivery  lines  reverse  their 
functions  and  the  pulp  remaining  in  the  box  is  withdrawn  and 
thrown  back  into  the  feed- vat.  Immediately  after  starting  this 
reverse  motion  of  the  pulp,  a  small  valve  is  partially  opened;  this 
admits  air  to  the  vacuum-drum,  and  is  so  regulated  that  the  mer- 
cury shall  not  register  over  six  to  nine  inches  vacuum.  The  correct 
height  for  each  kind  of  slime  has  to  be  ascertained  by  trial,  the 
object  being  to  have  it  as  low  as  possible  consistently  with  holding 
the  cake  in  contact  with  the  canvas.  This  is  an  important  point ; 
during  the  preliminary  experiments  it  was  found  that  when  the 
box  was  emptied  of  pulp  and  the  surfaces  of  the  cakes  exposed  to 
the  atmosphere,  the  passage  of  air  through  the  pores  rapidly  dried 
the  deposited  slime  and  caused  cracks,  which  rendered  a  perfect 
washing  of  the  residue  impossible.  By  lowering  the  vacuum  to 
a  point  sufficient  to  hold  the  cake  firmly  in  position  and  yet  cause 
a  minimum  of  air  to  pass  through  it,  the  difficulty  was  overcome 
and  the  cracking  prevented. 

When  the  box  is  nearly  empty,  the  spray  of  solution  is  turned 
on,  washing  down  the  sides  and  bottom,  and  removing  any  light 
slime  that  may  be  adhering  to  them. 

As  soon  as  the  last  of  the  pulp  has  been  removed,  the  main 
slime- valve  is  closed,  and  another  one  is  opened  to  admit  precipi- 
tated solution  to  the  pump,  by  which  means  the  filters  with  their 
adhering  cakes  are  again  completely  covered  with  liquor.  As 
soon  as  this  has  been  accomplished  the  air- valve  is  closed,  and  the 
full  vacuum  a  second  time  thrown  on  the  leaves,  so  as  to  draw  the 
wash-solution  through  the  cake  and  displace  the  dissolved  gold 
and  silver  contained  therein,  the  level  being  maintained,  as  before, 
so  as  to  keep  all  filtering  surface  covered  with  solution.  The 
time  required  for  this  wash  varies  with  the  thickness  of  the  cake 
and  the  quantity  of  solution  that  it  is  deemed  desirable  to  pass 


284  RECENT  CYANIDE  PRACTICE. 

through  it.  As  a  rule  it  is  found  that  by  drawing  through  an 
amount  of  liquor  equal  to  twice  the  amount  of  moisture  held  in 
the  cake  a  sufficient  displacement  is  effected  for  practical  require- 
ments. In  cases,  however,  where  the  solution  accompanying 
the  pulp  is  especially  rich  in  gold  and  silver,  a  wash  equal  in  quan- 
tity to  three  times  that  of  the  moisture  in  the  cake  may  have  to 
be  given.  When  the  washing  process  has  been  continued  long 
enough,  the  vacuum  is  again  lowered,  and  by  re-setting  the  3- way 
valves  the  remaining  solution  is  returned  to  the  vat  whence  it 
came.  (See  diagram  of  pump  connections,  Fig.  37.)  The  solution- 
valve  is  then  closed  and  water  is  thrown  through  the  common 
6-in.  pipe  until  the  filter  leaves  are  again  submerged;  the  vacuum 
is  put  on  for  a  few  minutes  to  displace  any  solution  that  may  be 
lying  in  the  pipes,  and  is  then  entirely  cut  off  and  the  valve  is 
opened;  water  then  enters  each  leaf  through  the  vacuum  con- 
nections, throwing  off  the  cake,  which  drops  to  the  bottom,  and 
cleansing  the  canvas  in  preparation  for  the  next  charge.  All  that 
now  remains  to  be  done  is  to  open  the  four  discharge-doors  and 
allow  the  contents,  both  water  and  hard  slime,  to  gravitate  to  the 
waste-dam,  open  the  end-doors,  and  wash  out  the  interior  thor- 
oughly with  the  hose.  After  closing  all  the  doors  the  filter  is 
ready  for  a  new  charge. 

Precipitated  solution  is  not  invariably  used  for  displacing 
the  valuable  moisture  in  the  cake ;  when  the  stock  of  solution  in 
circulation  through  the  plant  is  low,  it  is  brought  up  to  bulk  by 
using  water  instead  of  solution  for  this  purpose,  in  this  case  of  course, 
the  necessity  for  a  transference  after  washing  is  removed,  and 
when  the  requisite  number  of  tons  of  water  has  been  drawn 
through  the  cake  it  is  at  once  discharged,  together  with  all  the 
surplus  water  remaining  in  the  box. 

In  localities  where  water  is  scarce  it  is  not  necessary  to  waste 
all  the  water  standing  in  the  box  at  the  time  the  cake  is  thrown 
off;  before  dumping  the  residue,  this  water  may  be  decanted  to 
the  level  of  the  slime  and  stored  for  further  use. 

At  the  Minas  Prietas  plant  of  Charles  Butters  &  Co.,  com- 
pressed air  alone  is  used  for  dropping  the  cake,  and  the  residue  is 
run  out  to  the  dump  in  cars.  The  use  of  water  and  air  together, 
however,  as  already  described,  is  considered  an  improvement. 

WORKING  COSTS  AT  VIRGINIA  CITY.— The  two  chief 
items  of  expense  are  power  and  labor. 


FILTRATION  OF  SLIME.  285 

1. '  Labor. — As  already  stated,  the  filter  requires  only  one  man 
on  each  shift,  or  three  men  for  24  hours.  Taking  the  rate  of  wages 
as  $3  per  8-hour  shift,  the  labor  bill  will  amount  to  $9  for  handling 
150  tons  of  slime,  or  6c.  per  ton. 

2.  Power. : — The  principal  divisions  are,  the  6-in.  centrifugal, 
the  4-in.  centrifugal,  the  vacuum-pump,  and  the  service -pump  for 
supplying  the  tank  used  to  furnish  hose-pressure  for  sluicing  out 
the  residue.  The  water  used  for  filling  the  box  and  for  throwing 
off  the  cake  is  gravitated  into  the  plant  and  uses  no  power. 

The  6-in.  centrifugal  makes  1,440  r.p.m.,  and  when  running 
takes  25  h.p.  During  one  operation  of  the  filter  this  pump  runs 
as  follows: 

Operation  Minutes 

Filling  with  pulp 12 

Maintaining  pulp  at  one  level 5 

Emptying 12 

Filling  with  solution. 12 

Maintaining  constant  level 5 

Emptying 12 

Filling  with  water 12 

Total  .  .    70 


The  power  used  is  therefore  equivalent  to  29  h.p.  hr.  Power, 
as  supplied  by  the  Electric  Power  Company,  costs  approximately 
Ic.  per  h.p.  hr.,  so  the  cost  of  running  the  6-in.  pump  is  29c.  for 
each  charge,  or  1.54c.  per  ton. 

The  4-in.  centrifugal  pump  makes  1,600  r.p.m.  and  uses  10  h.p. 
During  one  operation  it  runs  34  min.,  equal  to  6.5  h.p.  hr.,  giving 
a  cost  of  5.6c.  for  each  charge,  or  0.3c.  per  ton  of  slime. 

The  vacuum-pump  runs  2  hr.  20  min.  for  each  charge,  tak- 
ing 8  h.p.  or  18.6  h.p.  hr.,  equal  to  18. 6c.,  or  Ic.  per  ton. 

The  water-service  pump  runs  about  10  hr.  per  day,  using  3 
h.p.,  or  30  h.p.  hr.,  which,  divided  over  150  tons  of  slime,  gives 
a  cost  of  0.2c.  per  ton. 

Thus  the  total  cost  of  power,  per  ton  of  slime,  is  as  follows: 


286  RECENT  CYANIDE  PRACTICE. 

Per  Ton 

6-in.  pump $0.0154 

4-in.  pump '. 0. 0030 

Vacuum-pump 0 . 0100 

Water-service  .  0.0020 


Total $0.0304 

3.     Repairs. — The  only  repairs  of  any  consequence  are  those 
to  the  6-in.  pump.     About  once  a  month  this  pump  needs: 

1  pair  of  liners $2 . 00 

1  disc 3 .  35 

1  shaft 1 . 80 

Mechanic's  labor  (2  hr.  at  50c.)    1 . 00 

Total $8.15 

This  for  4, 500  tons  gives  a  cost  of  0.2c.  per  ton.      The  running 
expenses  will  be: 

Per  Ton 

Labor $0.0600 

Power , 0. 0304 

Repairs . 0.0020 

Treating  leaves  with  acid 0. 0150 


Total $0.1074 

These  figures  were  compiled  when  only  one  filter-box  was  in 
use;  since  then  a  second  has  been  installed,  and  as  one  man  attends 
to  both,  the  cost  of  labor  has  come  down  to  3c.  per  ton,  showing 
a  total  working  cost  of  about  8c.  per  ton  of  slime. 

NOTES  ON  WORKING.— It  will  be  noticed  from  what  has 
been  said  about  washing,  that  the  practice  at  Virginia  City  at  this 
time  was  to  use  either  a  solution- wash  or  a  water- wash,  but  not  both 
on  any  given  charge.  The  reason  for  this  was  that  the  particular 
slime  being  treated  was  such  that  it  would  not  stand  being  twice 
exposed  to  the  action  of  the  air  without  cracks  forming  in  the 
cake.  This,  however,  is  not  the  case  with  all  slimes,  and  it  is 
usually  found  that  a  wash  of  solution  may  first  be  given  and  then 


FILTRATION  OF  SLIME. 


287 


a  further  period  of  water-wash.  Where  possible  the  latter 
arrangement  is  preferable,  because,  as  a  rule,  when  using  water 
alone  it  is  impossible  to  give  a  sufficient  quantity  for  effective  dis- 
placement without  overstocking  the  plant  with  weak  solution, 
which  finally  has  to  be  run  to  waste;  and  the  giving  of  an  ade- 
quate wash  with  barren  solution,  followed  by  a  quantity  of  water 
sufficient  to  compensate  for  the  daily  losses  in  the  stock,  and  thus 


SOlUTiOrt  AS6AY 
COMBINED. 

*    /    .05 
J.OO 

.0.95 
0.90 
0.85 
O.80 
O.TS 
O.TO 
O.65 
O.60 
O.55 
0.5O 
O.45 
O.^O 
0.35 
O.30 

o.as 
o.so 
O.I  5 
O.iO 
0.05 

o 

VIRGINIA     CITY    F  1  LT  E  R-  \A/A  S  H  1  Nl  G    CURVE. 
PRECIPITATED     SOLUTION    USE  D  T  H  RO  GH  O  UT. 
ASS/WS  -  QOLD*O.da  -   SI  L.VER     O.O7  OZ. 

15            3O           -45          €>O            T5            9O           IO5         IS.O          135          l5O         165          ISO  —  CUTS*. 

^ 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

^^^^ 

^^ 

~-         ., 

, 



• 

- 

Fig.  39. 

displacing  as  much  as  possible  of  the  cyanide  remaining  in  the 
cake,  generally  results  in  a  better  saving  of  cyanide  than  is 
obtained  by  the  Virginia  City  practice.  Another  method,  where 
it  is  not  possible  to  give  the  double  wash,  is  to  add  to  the  wash- 
solution  each  day  just  enough  water  to  maintain  the  balance  of 
stock  liquor  in  the  plant;  this  gives  more  uniform  results  than 
alternating  between  solution  and  water,  and  is  sometimes  prefer- 
able. 


288 


RECENT  CYANIDE  PRACTICE. 


With  regard  to  the  time  necessary  for  washing  the  cake,  the 
important  point  is  the  quantity  of  solution  that  is  drawn  through 
it;  in  a  given  time  this  varies  between  wide  limits  with  different 
classes  of  slime.  Fig.  39  and  40  are  two  charts  of  the  results  of 
the  wash  at  Virginia  City.  There  is  an  interval  of  two  or  three 
weeks  between  them.  In  one  of  them  solution  alone  was  used, 
and  in  the  other,  water.  The  rate  of  percolation  was  18  tons  per 


VIRG1NIACITY     Fl  l_T  E  R  -WA  S  H  I  M  G     CURVE. 
WATER    USED    THROUGHOUT. 

75  9O  105  l£O          135          1 5O         165          ISO 


/  .15 
I  .  10 
I  .05 
I  .00 
0.33 
O.90 
O.B5 
O.8O 
O.T5 
O.TO 
O.65 
O.6O 
O.55 
O.5O 


O.-1-O 
0.35 
O.30 
0.25 

o.ao 

O.  IS 

O.IO 

O.O5 

O 


15 


30 


^5        eo 


V 


Fig.  40. 


hour  in  each  case;  weight  of  dry  slime,  19  tons;  moisture  in  the 
cake,  40  per  cent.  The  samples  of  solution  were  caught  in  a  trap 
below  the  main  vacuum-pipe,  capable  of  holding  at  least  20  assay- 
tons,  which  quantity  was  used  for  each  assay.  Fig.  41  shows  a 
similar  chart,  made  at  the  Butters  Divisadero  Mines,  in  Salvador. 
Here  the  ore  is  ground  in  tube-mills  to  an  agitation  product  of 
which  about  85  per  cent  will  pass  a  200-mesh  screen,  and  the  whole 
«f  the  pulp  finally  reaches  the  filter.  In  this  instance  the  rate  of 


'  -  f 

^  ES  1  [ 

S1N«  ,UB4 

3U  E:  v 

souu- 

VA  s  ^ 

H  1  N  G 

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TER  t 

JOX. 

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O   MtNOTCS. 

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1  

5   60 

s. 

3.  SO 

\ 

3.-^O 

\ 

5.3O 

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\ 

3.  10 

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2.90 

S..8O 

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a.  50 

a.-=K> 

R."3O 

R.RO 

ft.  IO 

R.OO 

I.9O 

(.80 

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s 

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Fig.  41 


290  RECENT  CYANIDE  PRACTICE. 

percolation  was  28  tons  per  hour;  quantity  of  dry  slime,  18  tons; 
moisture  in  the  cake,  28  per  cent. 

When  considering  the  contents  of  the  solution  draining  from 
the  filter  just  before  discharging,  it  will  be  obvious  that  this  assay 
does  not  usually  represent  the  soluble  gold  and  silver  left  in  the 
cake.  Where  water  or  barren  solution  is  used  for  the  wash  no 
portion  of  the  residual  moisture  will  assay  as  high  as  that  which 
has  already  come  out,  and  the  average  of  it  will  be  much  lower; 
for  example,  if  the  last  solution  from  the  cake  should  assay,  let 
us  suppose,  20c.  per  ton,  the  moisture  remaining  behind  would 
probably  average  only  lOc.  or  less,  and  as  there  will  be  only  half 
a  ton  of  it  contained  in  a  ton  of  dry  slime  the  assay  of  the  residue 
would  be  raised  thereby  only  5c.  per  ton,  an  increase  that  could 
hardly  be  detected  by  the  assay  methods  ordinarily  in  use.  Five 
cents  per  ton,  however,  is  5c.,  whether  it  can  be  shown  by  the 
assay  or  not,  so  that  when  fixing  the  time  necessary  for  washing, 
it  will  be  well,  instead  of  depending  on  what  is  usually  known  as 
the  'washed  residue  assay,'  to  give  a  trial  wash  of  excessive  dura- 
tion once  or  twice  a  month,  taking  samples  of  the  issuing  solution 
periodically,  and  plotting  as  a  curve  the  figures  so  obtained;  it  will 
then  be  easy,  if  the  rate  of  percolation  is  known,  to  set  the  value 
recovered  at  any  given  point  against  the  cost  of  obtaining  it,  and 
in  this  way  to  determine  the  profitable  limit  to  place  on  the  period 
of  washing. 

The  question  of  saving  cyanide  will  not  enter  largely  into  this 
matter  of  wash-duration,  because  the  cyanide  can  only  be  dis- 
placed by  water,  and  the  amount  of  the  latter  used,  as  already 
pointed  out,  will  be  determined  by  the  daily  losses  of  moisture 
from  the  plant,  and  thus  cannot  be  varied  at  will  except  at  the 
expense  of  running  to  waste  weak  cyanide  solution  from  some 
other  part  of  the  plant.  Several  curves  showing  the  progressive 
elimination  of  cyanide  from  the  cake  have  been  made,  but  as  they 
were  not  consistent  with  the  gold  and  silver  curves  made  at  the 
same  time  they  are  not  given  here,  and  the  matter  is  still  under 
investigation. 

The  following  is  a  table  of  the  time  needed  (with  a  f-in.  cake) 
for  the  various  operations,  taken  directly  from  the  filter  log-book 
at  Virginia  City: 


FILTRATION  OF  SLIME.  291 

Hr.  Min. 

Filling  and  taking  on  cake 0         45 

.  Removing    surplus    pulp     and    re-filling    with 

solution 0         25 

Drawing  wash-solution  through  cake 1         15 

Replacing  solution  by  water,  throwing  off  cake, 
discharging,  sluicing  out,  and  re-closing 
doors 0  35 

Total  time  of  operation 3  0 

The  percentage  of  moisture  held  by  the  cake  before  being 
detached  from  its  support  is  from  35  to  40%  in  this  case, 
though  the  average  for  an  ordinary  slime  would  be  nearer  33  per 
cent. 

The  box  contains  94  filter-leaves,  and  each  leaf  carries  about 
400  Ib.  dry  slime,  giving  a  capacity  of  19  tons  at  each  operation, 
or  150  tons  per  24  hours.  With  certain  kinds  of  slime  the  capacity 
of  a  filter  of  this  size  may  be  as  much  as  25  tons  per  charge,  mak- 
ing 200  tons  or  more  per  24  hours. 

The  consistence  of  the  pulp  fed  to  the  filter  has  an  important 
bearing  on  the  efficiency  of  the  latter;  the  thicker  it  is,  the  better 
it  will  suspend  fine  sandy  material  and  form  a  homogeneous  mass 
giving  a  uniform  cake,  and  also  the  less  time  it  will  need  to  form 
the  cake  and  therefore  the  greater  will  be  the  capacity  of  a  given 
filter  unit  in  a  given  time.  Of  course,  there  is  a  limit  in  the  con- 
sistence, beyond  which  the  thickness  would  cause  trouble  by 
clogging  the  pipe-lines,  and  a  useful  point  to  aim  at  is  a  specific 
gravity  of  from  1.3  to  1.4. 

At  the  start  there  was  one  point  in  connection  with  the  work- 
ing of  the  filter  that  was  not  apparent.  It  was  found  that  after 
a  few  months  the  permeability  of  the  leaves  began  to  grow  less, 
thus  necessitating  a  longer  time  for  loading  and  also  for  passing 
the  wash.  After  a  careful  examination,  it  was  traced  to  a  forma- 
tion of  calcium  carbonate  in  the  fibre  of  the  canvas  and  more 
especially  on  its  exterior  surface.  This  was  found  to  be  easily 
removed  by  immersing  the  leaves  in  a  dilute  solution  of  hydrochloric 
acid.  A  rectangular  wooden  vat  was  prepared  capable  of  holding 
seven  or  eight  leaves  at  a  time,  and  this  was  filled  with  a  solution 
containing  about  two  per  cent  commercial  muriatic  acid  in  water. 
Seven  leaves  are  removed  each  day,  their  places  being  filled  by 


r  SLUICE  ooon.% 

G  IZ    P   O   VAUVCfc 

H  DI%CHAMCC  non 

J  ACIC  WA»M    TAN 


R       OlSCMAWOt  WVATCI 

S     CE.NTKIFUG.AI-  rui 
T     SUCTION  rnoM  ftu» 


1 2O  FRAME  VACUUM  FILTER  PLANT- 


Fig.  42. 


FILTRATION  OF  SLIME.  293 

spares.     They  are  placed  in  the  acid  bath  and  allowed  to  remain 
for  about  six  hours,  at  the  end  of  which  time  they  are  removed, 
drained,  and  placed  in  a    water-tank  to  stop  the  action  of    the 
acid.     In  this  way  each  leaf  is  treated  about  twice  per  month. 

If  this  is  not  sufficient  to  restore  the  leaves  to  a  perfect  working 
condition,  the  strength  of  the  acid  may  be  increased  to  five  or  six 
per  cent ,  and  a  vacuum  arrangement  attached  to  them  for  drawing 
the  solution  through  the  fibre  repeatedly,  until  all  the  deposit  is 
removed.  Instead  of  continually  adding  acid  tore-strengthen  the 
bath,  it  is  better  to  turn  the  whole  liquor  to  waste  at  short  inter- 
vals, because  it  is  liable  soon  to  get  charged  with  salts,  which,  if 
not  properly  washed  out  from  the  leaves  with  water,  may  be 
precipitated  in  the  fibre  of  the  canvas  when  next  it  comes  in  con- 
tact with  the  alkaline  solution. 

To  get  the  highest  efficiency  from  this  filter  it  is  important  to 
make  the  transfer  of  pulp  and  solution  as  rapidly  as  possible,  and 
this  for  two  reasons:  (1)  It  materially  increases  the  capacity  of 
a  given  filter-unit  and  thus  decreases  the  working  costs  per  ton  of 
slime  in  the  item  of  labor,  and  (2)  it  lessens  the  liability  of  the 
cake  to  crack  when  exposed  to  the  air,  and  in  the  case  of  slime  that 
has  an  exceptional  predisposition  to  crack,  it  renders  it  possible 
to  give  a  double  wash,  of  solution,  followed  by  water,  when  other- 
wise only  a  single  wash  could  have  been  applied. 

For  a  rapid  transfer  of  the  pulp  and  solution  the  gravity  system 
of  filling  and  emptying  the  box  gives  excellent  results.  The 
general  arrangement  is  shown  in  Fig.  42,  though  there  a  water- 
wash  only  is  provided  for.  Usually  a  second  vat  at  the  level  of  C 
is  provided  to  receive  the  surplus  solution,  and  also  a  third  vat  for 
surplus  water  where  the  double  wash  is  given  and  where  the  water 
is  sufficiently  valuable  to  be  saved  for  re-use.  The  method  of 
working  is  to  fill  the  box  with  pulp  by  gravity  through  two  or 
more  6-in.  pipe-lines  from  the  feed- vat  above;  then  after  taking 
on  the  cake  to  let  out  the  surplus  through  the  discharge  gates  into 
vat  C,  which  has  a  light  stirring  gear  to  keep  the  slime  in  sus- 
pension while  it  is  being  thrown  back  by  a  4-in.  centrifugal  pump 
to  the  feed-vat  above.  The  same  process  is  then  repeated  with  the 
wash  solution,  and  again  with  the  water  if  necessary,  each  in  turn 
being  thrown  back  to  the  higher  level  by  the  same  4-in.  pump. 
In  this  way  the  box  may  be  filled  in  four  or  five  minutes  and  emp- 
tied in  three  minutes,  so  that  the  cake  is  exposed  to  the  air  only 


s 


*  j  I  z  c  O-tf 


FILTRATION  OF  SLIME,  295 

about  eight  minutes  for  each  transfer;  this  is  a  great  advantage 
where  a  slime  shows  a  tendency  to  crack.  The  arrangement  is 
chiefly  applicable  where  the  mill-site  is  on  the  side  of  a  hill ;  for  level 
sites  the  pump-system  is  usually  more  suitable.  By  the  latter,  of 
course,  results  similar  to  those  of  the  gravitation  system  may  be 
obtained  by  using  a  sufficiently  large  pump  and  pipe-line,  but 
where  the  site  is  favorable  to  gravitation  this  has  the  advantage 
of  a  rapidity  of  transfer  without  the  sudden  switching  on  and  off 
of  a  heavy  load  at  short  intervals  with  its  attendant  strains  on 
the  source  of  power  and  the  machinery  in  general,  the  power 
used  being  comparatively  small  in  amount  and  evenly  distributed 
over  a  long  period  of  time.  The  method  has  been  in  use  at  the 
cyanide  plant  of  the  Butters  Copala  Mines,  in  Sinaloa,  Mexico, 
for  over  12  months  and  has  given  entire  satisfaction. 

The  Butters  patent  filter  is  now  well  past  the  experimental 
stage,  and  its  advent  may  be  said  to  mark  the  beginning  of  a  new 
era  in  the  history  of  ore-slime  treatment,  and  to  open  up  possi- 
bilities unknown  a  few  years  ago.  The  time  may  even  be  not  far 
distant  when  slime  from  gold  ores  will  be  treated  by  cyanide 
solution  directly  in  the  vacuum-filter,  so  that  all  the  expensive 
agitation  and  decantation  machinery  now  in  use  can  be  discarded. 

It  would  perhaps  be  too  sanguine  to  hope  that  the  slimes  of 
silver  ore  may  also  be  treated  in  the  same  way  in  the  near  future, 
because,  as  far  as  our  present  experience  goes,  such  ore  requires 
a  much  longer  time  in  contact  with  cyanide  than  would  be  prac- 
ticable in  any  filter,  but  as  soon  as  some  means  is  found  of  accel- 
erating the  solution  of  silver  in  cyanide,  then  there  is  little  doubt 
that  agitation  and  decantation  will  give  place  to  treatment  by 
leaching  in  vacuum-filters. 


OLD  AND  NEW  METHODS  AT  GUANAJUATO, 

MEXICO 

BY  T.  A.  RICKARD 

(June  29,  1907) 

Reference  has  been  made  to  the  milling  practice  of  the  Guana- 
juato Reduction  &  Mines  Co.  in  speaking  of  the  Bustos  plant. 
It  deserves  further  consideration.  Although  the  property  was 
acquired  in  January,  1904,  it  was  not  until  February,  1905, 
that  it  was  decided  to  build  80  stamps,  rushing  the  erection  of  five 
of  them  so  as  to  afford  experimental  data  during  the  construction 
period.  Many  tests  on  a  large  as  well  as  a  small  scale,  had  already 
demonstrated  that  a  high  extraction  of  both  silver  and  gold  could 
be  obtained  from  the  ore  by  cyanidation,  and  the  experimental 
plant  became  of  great  service  in  testing  ores  from  different  parts  of 
the  company's  properties,  as  well  as  to  suggest  the  detail  manipu- 
lation best  adapted  for  the  main  plant,  then  under  construction. 
The  mines  are  a  mile  from  Guanajuato,  and  there  are  no  streams 
available  for  disposal  of  the  tailing;  nor  is  there  the  space  necessary 
for  accumulating  residue  on  a  large  scale.  It  became  necessary  to 
discharge  the  tailing  into  the  main  stream  of  the  district  one  mile 
from  the  mines,  and  this  meant  the  transportation  of  all  ores 
through  the  heart  of  the  City  over  an  expensive  railroad  system 
or  the  complete  separation  of  the  stamp-mill  from  the  cyanide  plant, 
the  latter  to  be  placed  upon  the  main  stream. 

The  Homestake  system,  of  conveying  the  tailing  in  a  cast-iron 
sewer-pipe  was  adopted;  it  is  an  8-in.  water-pipe  of  bell  and 
spigot  type,  asphalted,  laid  for  its  first  few  hundred  feet  at  a  grade 
of  3%,  then  flattening  to  2J%.  As  it  was  desirable  to  settle  and 
return  for  re-use  as  much  of  the  water  coming  from  the  concen- 
trators as  possible,  allowing  the  thick  pulp  only  to  pass  through 
the  pipe,  and  to  determine  to  what  point  such  thickening  was 
possible,  several  hundred  feet  of  the  pipe  to  be  employed  in  this 
work  were  put  together  and  laid  out  upon  the  actual  grade. 
Arrangements  were  made  to  circulate  any  given  quantity  of  sand, 
crushed  in  the  stamps  of  the  experimental  plant  already  installed, 


OLD  AND  NEW  METHODS  AT  GUANAJUATO.     297 

through  this  pipe-line  at  any  desired  degree  of  dilution.  Pulp  was 
first  tried  at  a  normal  dilution  of  8  of  water  to  1  of  sand,  just  as  it 
came  from  the  tail  of  the  concentrator  tables ;  the  water  was  then 
decanted  by  successive  steps,  thickening  the  pulp,  and  several  runs 
were  made  under  these  varying  conditions.  It  was  desired  to 
remove  a  maximum  of  one-half  of  the  original  water,  and  in  the 
experiments  the  8  to  1  pulp  was  reduced  to  2 . 5  to  1 ,  and  so  success- 
fully that  not  only  was  the  pipe  not  clogged  with  sand,  but  the  pulp 


m  • 


f 

/ 


Fig.  44.     Pipe  for  Conveying  Tailing. 

at  that  thickness  had  such  rapidity  of  flow  that  it  readily  carried 
nuts  and  other  heavy  objects  without  interrupting  the  stream. 
Tests  made  by  Mr.  Carlos  Van  Law  proved  that  pulp  which  has 
passed  through  a  30-mesh  screen,  with  water  in  the  proportion  of 
7^  to  1,  will  flow  through  a  launder  of  square  cross-section,  made  of 
rough  boards,  set  on  a  grade  of  1J%,  With  a  V-shaped  wooden 
launder,  such  pulp  wrill  flow  at  less  grade  and  with  less  water.  The 
area  of  the  wet  perimeter  is  the  factor. 


298  RECENT  CYANIDE  PRACTICE. 

This  problem  settled,  the  process  was  outlined  as  follows:  The 
ore  is  transported  over  a  railroad  from  the  mines  in  hopper-bottom 
cars,  which  discharge  into  a  large  bin  at  the  crusher  plant. 
It  is  then  passed  through  a  No.  5  D.  Gates  crusher  to  2-in.  size, 
discharging  over  a  picking-belt  for  removal  of  waste,  then  re- 
crushed  by  a  short-head  No.  4  Gates  crusher  to  1-in.  ring,  then 
removed  by  conveyor-belts  to  the  mill-bins,  where  it  is  distributed 
by  cars,  this  (owing  to  cheap  labor) ,  proving  more  economical  than 
the  use  of  a  system  of  conveyor-belts  over  the  top  of  a  bin  with 
automatic  trippers.  The  mill-bin  has  a  capacity  for  five  days, 
which,  together  with  the  large  bin  at  the  crusher  plant,  affords 
sufficient  storage  of  ore. 

The  ore  is  then  crushed  under  eighty  1,050-lb.  stamps  of 
Allis-Chalmers  make.  The  mortars  are  set  on  a  concrete  foundation, 
the  anvil  block  being  cast  as  an  integral  part  of  the  mortar. 
The  latter  has  a  steel  liner,  two  inches  thick,  but  there  is  13.5  in. 
of  metal  below  the  liner.  Between  the  anvil-block  and  the  con- 
crete a  quarter-inch  sheet  of  rubber  is  spread.  The  mortar  has  a 
broad  base — 36  in.  wide — provided  with  strong  ribs  at  the  sides. 

The  30-mesh  pulp  resulting  from  the  stamping  is  concentrated 
over  Wilfley  tables,  a  considerable  amount  of  middling  produced 
being  removed  for  re-grinding  in  an  Abbe  tube-mill  and  subse- 
quent treatment  over  separate  concentrator  tables.  The  tailing 
from  all  the  machines  drops  into  concrete  launders  and  passes  to  the 
cones  where  about  half  of  the  water  is  removed  for  use  in  the 
mill.  The  thickened  tailing  then  enters  an  8-in.  cast-iron  pipe, 
laid  on  the  grade  above  mentioned,  and  goes  to  the  classifiers  in  the 
Hacienda  Flores,  situated  upon  the  main  channel  of  the  Guana- 
juato river.  The  classifiers  are  all  of  the  Homestake  type,  two 
sets  of  cones  being  used,  the  lower  one  taking  the  bottom  product 
of  the  upper.  The  overflow  from  both  sets  of  cones  goes  to  the 
slime-plant,  the  lower  cone  having  an  ascending  current  of  water. 

The  sand  coming  from  the  bottom  of  the  lower  cones  is  dis- 
tributed, by  the  Butters  &  Mein  device,  into  either  of  two 
receiving- vats,  each  of  350  tons  capacity.  These  were  planned  to 
serve  an  ultimate  capacity  of  500  tons  daily,  with  the  slime  sep- 
arated. 

The  receiving-vats  are  alternately  filled  and  drained,  the 
discharge  being  made  through  bottom  gates  onto  ascending 


OLD  AND  NEW  METHODS  AT  GUANAJUATO.     299 

conveyor-belts,  which  pass  over  the  centre  of  the  line  of  eight 
leaching- vats,  each  of  the  same  size  as  the  receiving- vats.  In  these 
a  14-day  treatment  is  given  with  0.5%  cyanide  solutionvthe  sand 
being  then  washed  and  ultimately  discharged  on  conveyor-belts 
(running  under  the  vats) ,  which  deliver  either  into  the  river  during 
the  rainy  season,  or  to  elevated  storage-piles  during  the  dry  season, 
to  be  sluiced  during  the  succeeding  rainy  season. 

The  slime  from  the  classifying  cones  is  treated  by  agitation 
with  mechanical  stirring  and  large  centrifugal  pumps,  which  draw 
from  the  bottoms  of  the  vats  and  discharge  over  the  tops,  the  total 
time  of  treatment  being  four  days.  After  the  final  wash  the  slime 
is  pumped  into  settling-vats  30  ft.  high,  where  a  further  decantation 
occurs  before  the  slime  is  discharged,  with  a  very  small  percentage 
of  moisture,  into  the  river. 

The  entire  plant,  both  the  stamp-mill  and  cyanide  annex,  is 
designed  so  that  it  can  be  doubled,  when  the  stamp-mill  will  take  a 
back-to-back  form,  80  stamps  with  their  concentrators  being  on 
either  side  of  the  bins.  The  classifying-cones  and  the  receiving- 
vats  of  the  cyanide  annex  are  of  sufficient  size  already  for  a  500-ton 
plant,  it  being  necessary  only. to  add  another  line  of  eight  leaching- 
vats  and  the  corresponding  slime-vats  to  bring  the  cyanide  plant 
to  the  larger  capacity  mentioned. 

For  roofing,  corrugated  galvanized  iron  on  a  steel  frame  is  pre- 
ferred. As  there  is  no  load  of  snow  to  fear,  it  is  possible  to  use  a 
light  roof-truss.  The  native  tile  is  cheaper,  but  it  requires  a 
heavier  construction,  and  does  not  afford  as  complete  protection. 
The  Northerner  will  remark  the  lavishness  of  the  masonry  about 
the  mines  and  mills  in  Mexico.  It  is  the  cheapest  kind  of  construc- 
tion and  the  native  wood  is  usually  poor;  it  will  twist  and  untwist 
as  the  dry  and  wret  seasons  succeed  each  other,  making  it  an 
unsatisfactory  structural  material. 

At  the  time  of  my  visit  there  were  120  stamps  in  operation 
in  the  Guanajuato  district,  and  there  were  205  tons  being  treated 
daily  by  cyanidation  and  25  to  30  tons  by  patio.  Thus  does  the 
new  drive  out  the  old.  In  1887  there  were  34  patios  at  work; 
now  there  are  only  two. 

In  regard  to  cost  in  the  patio  process,  I  have  the  following  data 
from  the  Hacienda  de  San  Julio  at  Pachuca: 


Fig.  45.     Bustos  Mill,   in  Course  of  Construction. 


OLD  AND  NEW  METHODS  AT  GUANAJUATO.     301 

Pesos 

Crushing,  to  pass  60-mesh  in  Chilean  mills,  with 

overflow  discharge 3.60 

Maintenance    0.50 

Salt.    5%,  or  50  kg.  per  ton .. 1.75 

Copper    sulphate.     Loss,  0.5%    - 1.25 

Mercury.     Loss,  1J  kg.  for  each  kilogram  of  silver  4.38 

Transport  from  the  mine 1.08 


Total 12.56 

The  ore  is  bought  on  the  dump,  therefore  the  cost  of  transport  is 
included.  Salt  costs  35  pesos  per  ton ;  copper  sulphate  250  pesos  per 
ton,  and  mercury  3.41  pesos  per  kilogram.  The  average  losses  for 
the  year  were  1 . 1 8  to  1 . 50  kilogram.  Per  kilogram  of  silver  extracted ; 
the  loss  of  silver  being  6.13  to  10.92%  on  the  clean  ore,  and 
15.83  to  29.13%  on  the  galena  ore.  The  patio  process  waits  on 
the  completion  of  the  chemical  reactions,  and  it  is  therefore  con- 
tinued until  extraction  ceases.  Time  is  not  considered,  in  winter 
it  requires  20%  longer  by  reason  of  the  lower  temperature  of 
the  air. 

At  Parral,  in  Chihuahua,  with  the  Russell  process,  using 
hyposulphite,  the  cost  of  lixiviation  and  roasting  is  11  pesos,  but 
the  recovery  is  not  as  high  as  it  is  with  amalgamation  in  the  patio, 
where  the  cost  is  1 1  to  14  pesos,  varying  according  to  the  manganese 
content  of  the  ore. 

At  Pachuca,  by  Mexican  methods,  the  cost  of  mining  and 
sorting  ore  amounts  to  15  pesos  per  ton;  the  transport  to  the  patio 
and  the  treatment  there  makes  a  further  cost  of  14  pesos,  not 
including  losses  or  the  expense  of  marketing  the  product.  By 
stamp-milling,  pan  amalgamation,  and  concentration,  the  cost  at 
Guanajuato  was  8  pesos;  and  now  by  stamp-milling  and  cyanidation 
the  cost  is  5.85  pesos.  That  of  mining  and  development  is  3.50  to 
4.50  pesos,  so  that  the  total  present  cost  is  about  10  pisos,  or  $5  per 
ton. 

At  the  time  of  my  visit  there  were  about  200  men,  women,  and 
children  in  the  Anglo-American  colony  at  Guanajuato,  the  Amer- 
ican element  predominating.  Of  the  125  men  employed,  75  to  80 
were  technical  men,  of  good  training.  This  made  a  strong  piece  of 
mental  machinery  for  industrial  development. 


CYANIDE      PRACTICE     AT     THE 

MILLS 


HOMESTAKE 


BY  F.  L.  BOSQUI 

(July  6,  1907.) 

Apropos  of  recent  descriptions  of  filtering  processes,  including 
the  Butters,  Moore,  and  Ridgway  systems,  some  account  of  present 
Homestake  practice,  compiled  from  notes  taken  on  a  recent  visit 
to  the  property  may  be  of  interest.  By  way  of  preface,  and 
to  refresh  the  reader's  mind  as  to  the  main  facts,  the  Homestake 


Fig.  46.     Precipitation-Presses. 

plants  at  Lead,  in  the  Black  Hills  of  South  Dakota,  consist  of  six 
stamp-mills,  containing  an  aggregate  of  1,000  stamps  and  crushing 
about  4,000  tons  per  day.  The  most  interesting  feature  of  the  mill- 
practice  is  the  amalgamation.  Each  battery  is  provided  with 


CYANIDE  PRACTICE  AT  THE  HOMESTAKE.      303 

four  full-sized  plates,  in  series,  each  plate  being  54  by  144  in.  and 
J  in.  thick.  The  first  is  plain  copper,  the  last  three  are  silver-plated. 
This  addition  of  three  silver  plates,  giving  to  each  10  stamps  of  the 
Amicus  (240-head)  mill,  a  total  plate-area  of  600  sq.  ft.,  and  to  the 
other  mills  an  average  of  360  sq.  ft.  per  10  stamps,  is  a  compara- 
tively recent  innovation,  and  has  proved  an  excellent  one,  increasing 
the  recovery  by  amalgamation  approximately  $200,000  per  year 


Fig.  47.     Screw  End  of  the  Slime-Press.    * 

above  the  annual  recovery  when  only  one  12-ft.  plate  was  used. 
The  saving  by  amalgamation  is  between  70  and  75  per  cent. 

The  leachable  portion  of  the  tailing  from  the  stamp  mills  (640 
stamps),  consisting  mostly  of  ore  from  the  deeper  levels,  is  treated, 
after  slime  separation,  at  the  Lead  plant,  known  as  Cyanide  No. 
1.  This  plant  has  a  capacity  of  about  1,800  tons  per  day.  The 
oxidized  surface  ore  is  crushed  in  the  mills  at  the  north  end  of  the 


304 


RECENT  CYANIDE  PRACTICE. 


property  (360  stamps)  and  the  sand  treated  in  the  annex  known 
as  Cyanide  No.  2,  at  Gayville,  two  miles  distant  from  Lead.  This 
smaller  plant  handles  about  800  tons  per  day.  Both  plants  were 
designed  and  installed  under  the  direction  of  C.  W.  Merrill,  who 


Fig.  48.     Discharge  from  Two  Presses. 

.devised  the  process  and  who  recently  installed  the  filter-press 
slime-plant  to  be  described  herewith.  The  practice  at  Cyanide 
No.  1  has  been  well  described  by  Mr.  Merrill  himself*  and  needs 
no  further  comment. 


*Trans.  Amer.  Inst.  Min.  Eng.,  New  York  meeting,  1903. 


CYANIDE  PRACTICE  AT  THE  HOMESTAKE.      305 

The  system  of  slime  separation  in  use  at  these  plants  has  been 
•criticized  by  some  of  the  advocates  of  South  African  methods  as 
less  effective  than  the  old  pointed-box  system.  But  at  the  Home- 
stake,  the  choice  of  cone-classification  has  been  emphatically  jus- 


Fig.  49.     The  Great  Open-Cut  of  the  Homestake. 

tified  by  the  results.  An  elaborate  sizing  was  not  necessary  and 
was  not  attempted.  Exigencies  of  first  cost,  space,  labor,  etc., 
precluded  double  treatment;  and  to  make  the  enterprise  profit- 
.able,  it  was  essential  that  all  the  sand  be  treated  as  a  separate 


306  RECENT  CYANIDE  PRACTICE. 

product,  and  in  one  operation.  To  those  familiar  with  the  diffi- 
culty of  obtaining,  without  re-handling  the  pulp,  a  uniform  charge 
of  hydraulically  distributed  sand  that  will  leach  rapidly,  the 
appended  figures  will  seem  incredible. 

The  leachable  sand  has  the  following  average  texture: 

Coarse  (remaining  on  100  mesh)  30  per  cent. 

Middling  (100  to  200  mesh)  32  per  cent. 

Fine  (passing  200  mesh)  38  per  cent. 

Through  this  product  the  solution  percolates  at  the  rate  of 
from  three  to  four  inches  per  hour. 

When  we  consider  that  all  the  separated  slime  passes  through 
200  mesh,  and  that  this  product  is  in  so  fine  a  state  of  division 
that  90%  of  its  value  is  extracted  in  six  hours  by  filter- 
pressing,  the  merits  of  the  Homestake  classification  system 
require  no  further  emphasis.  The  cost  of  treatment  at  Cyanide  No. 
1,  which  Mr.  Merrill  gave  in  1903  as  35c.,  has  since  been  reduced 
to  26c.  per  ton.  At  Cyanide  No.  2,  the  product  treated  is  much 
lower  in  grade,  averaging  only  85c.  per  ton.  This  plant  was  the 
more  recently  constructed  of  the  two,  and  is  the  more  perfect, 
not  only  in  its  arrangement ,  but  in  its  facilities  for  maintaining 
a  low  cost  of  treatment.  A  summary  of  the  operating  cost  for 
six  months  is  given  below. 

COST  .RECORD  AT  HOMESTAKE  CYANIDE  MILL  NO.  2, 
FOR  LAST  SIX  MONTHS  OF  1906. 


July.     Aug.     Sept. 


Oct.      Nov.      Dec. 


Total  tons  of  sand  treated 24,913  25,644  24,496  24,352  24,190  25,398 

Total  operating  cost $4,165  $4,609  $3,94l|  $4,380|  $4,122  $3,274 


Cost  per  ton,  classification .  . 
"  "  "  treatment  .... 
"  "  "  precipitation 


$0.018  $0.017  $0.017'  $0.017  $0.016  $0.023 
0.094     0.093     0.079     0.086     0.090     0.080 


0.026     0.021     0.022 

power j    0.021     0.041     0.031 

assaying,  refining,  etc ,1    0.008     0.007,    0.012 


0.021 
0.048 
0.008 


0.019  0.021 
0.035  0.037 
0.010  0.007 


Total  cost  per  ton  treated |  $0.167|  $0.179  $0.161  $0.180  $0.170  $0.168 

AVERAGE  SIZING  OF  SAND. 

Total  tons  treated  for  the  six  months.         148,993     Per  cent.  Mesh. 

Total  operative  and  treatment  cost        $25,493.64     37.55  coarser  than  .  . .  100 

Average  cost  per  ton  treated  $0.171   23.00  between 100  and  200 

39.45  finer  than .  .  200 


I  have  mentioned  the  slime  separation  as  a  most  interesting 
feature   of  these  plants.     Another  novel   feature   is   the   periodic 


CYANIDE  PRACTICE  AT  THE  HOMESTAKE.       307 

introduction  of  air  into  the  pulp  for  the  purpose  of  providing 
oxygen  to  the  subsulphide  of  iron  (pyrrhotite) — one  of  the  most 
troublesome  constituents  of  the  ore — and  so  maintaining  the  dis- 
solving power  of  the  solution,  which  would  otherwise  be  robbed 
of  its  oxygen  by  the  iron.  Both  of  these  big  plants  are  remarkable 
for  the  order  and  neatness  exhibited  in  every  department.  Opera- 
tions have  been  reduced  to  so  simple  a  system  that  they  seem  to  be 
working  automatically;  yet  if  one  glances  behind  the  scene,  he 


Fig.   50.     Triplex  Solution  Pump  with  Motor  Double-Wound  to  Give  Full 
and  Half  Speeds.     Shows  Effluent  Lixiviant  from  Slime-Presses. 

rinds  an  able  corps  of  assistants  continually  studying  special  prob- 
lems, looking  to  the  reduction  of  costs  and  increased  efficiency. 

From  the  two  leaching  plants,  about  1,600  tons  of  slime  have 
been  run  to  waste,  of  an  average  value  of  between  40c.  and  $1.20 
per  ton.  In  working  out  a  method  for  treating  this  product,  Mr. 
Merrill  considered  the  various  slime  processes  now  in  favor,  but 
discarded  them  all  as  unsuited  to  Homestake  conditions.  In 
^treating  an  80c.  slime,  a  system  requiring  the  two  operations  of 


308 


RECENT  CYANIDE  PRACTICE. 


agitation  and  filtration  in  separate  vessels  was  not  to  be  thought 
of;  and  the  only  device  in  which  treatment  and  filtration  could 
be  performed  in  one  operation  was  the  filter-press;  but  the  cost 
of  operating  the  old  type  of  filter-press  was  prohibitive,  and  this 
condition  led  to  the  development  of  what  is  known  as  the  Merrill 
press,  which  essentially  differs  from  the  old  type  in  that  it  can  be 
discharged  without  drawing  the  plates  and  frames  apart.  Several 
good  descriptions  of  the  Merrill  press  and  process  have  appeared 


Fig.  51.     Front  View  of  Battery  of  20-ton  Slime  Presses. 


in  the  mining  periodicals  and  I  shall  not  attempt  here  more  than 
a  brief  account  of  the  plant. 

At  the  beginning,  a  10-ton  press  with  4  by  6-ft.  frames  was 
installed  for  experimental  purposes  and  was  in  use  continuously  for 
18  months.  In  one  run  131  charges  were  treated,  on  which  the 
following  data  are  available: 

Average  value  of  slime  before  treatment,  91c. ;  after  treatment, 
lOc.  Extraction  by  assays,  per  ton  treated,  90  per  cent  or  81c. 


CYANIDE  PRACTICE  AT  THE  HOMESTAKE        309 

per  ton.  Recovered  in  precipitate,  per  ton  treated,  91  per  cent 
or  83c.  per  ton.  The  treatment  was  simply  lixiviation  in  the 
press,  without  agitation.  Amount  of  solution  used  to  leach  one  ton 
of  slime,  0.73  tons;  amount  of  water  used  for  sluicing,  four  tons  to 
one  ton  of  slime;  thickness  of  cake,  4  inches. 

The  large  plant  recently  started,  is  situated  at  Deadwood. 
The  slime,  after  partial  de watering,  in  cone-bottom  clarifying  vats, 
which  reduces  the  proportion  of  water  to  solid,  to  the  ratio  of 
three  to  one,  is  conveyed  in  two  pipe-lines  to  the  slime-plant,  as  fol- 
lows: A  12-in.  pipe  carries  it  from  Cyanide  No.  1,  a  distance  of  3f 
miles,  at  a  minimum  grade  of  1J%;  a  10-in.  pipe  carries  it 
from  Cyanide  No.  2,  a  distance  of  two  miles,  at  a  grade  of  H%." 
The  plant  is  built  on  a  steep  hillside  and  consists  of  five 
levels.  The  uppermost  contains  the  apparatus  for  slaking  lime 
and  feeding  it  automatically  into  the  stream  of  slime ;  the  next 
department  contains  two  large  cone-bottom  accumulation- vats ;  the 
next  floor  is  occupied  by  the  solution  storage-vats  and  precipita- 
tion-presses ;  the  next  by  the  slime-presses ;  and  the  lowest  by  the 
precipitation-vats  and  dumps. 

Two  small  vats  are  provided  for  slaking  lime.  Their  con- 
tents are  drawn  as  required  to  a  screen-covered  box  where  the 
undissolved  lumps  are  separated.  This  box  overflows  into  an  agita- 
tor, from  which  the  milk-of-lime  is  continuously  discharged  into 
the  main  slime-stream  at  the  rate  of  5  Ib.  lime  per  ton  of  slime. 
The  two  sludge  storage- vats  are  26  ft.  diam.  and  24  ft.  deep  with 
a  47°  conical  bottom.  The  discharge  from  the  sludge-vats  passes 
directly  to  the  filter-presses  under  a  pressure  of  about  30  Ib. 
through  a  10-in.  main,  which  extends  through  the  whole  length  of 
the  press-building.  Between  each  pair  of  presses  this  main 
branches  into  a  longitudinal  10-in.  distributing  pipe,  which  in 
turn  sends  two  4-in.  branches  to  each  press.  These  small  branches 
communicate  with  a  continuous  channel  in  the  press  at  the  centre 
of  the  top,  4  in.  diam.,  by  means  of  which  the  slime  passes  to  the 
filter-chambers.  Other  channels  are  provided  as  follows  :  One  at 
each  upper  corner,  2^  in.  diam.,  for  the  entrance  and  exit  of  air; 
one  at  each  lower  corner,  of  same  diameter,  for  entrance  and 
exit  of  solution;  and  one  large  continuous  channel  extending 
along  the  centre  of  the  bottom,  by  means  of  which  the  spent 
slime  is  sluiced  out.  This  channel  is  6  in.  diam.,  and  along  its 


310 


RECENT  CYANIDE  PRACTICE. 


top  is  suspended  a  3-in.  pipe  extending  the  length  of -the  press. 
This  pipe  is  provided  with  92  nozzles,  1  in.  long  and  5/32  in.  diam., 
each  of  which  delivers  a  stream  into  one  of  the  4-in.  chambers, 
under  a  head  of  about  50  Ib.  By  a  special  mechanism,  a  recipro- 
cating motion  is  imparted  to  this  pipe,  causing  it  to  revolve 
through  an  arc  of  210°,  so  that  each  small  nozzle  plays  against  the 
compact  slime  cake,  removing  the  cake  completely  and  cleansing 
the  compartment  in  about  45  minutes.  The  discharged  slime 


Fig.  52.     Merrill  Zinc-Dust  Precipitation  Press. 


leaves  the  press  through  the  crescent-shaped  space  between  the 
4-in.  pipe  and  the  6-in.  channel,  the  latter  being  sealed  during  the 
operations  of  filling  and  leaching. 

The  operations  within  the  press  consist  of  leaching  with  solu- 
tions of  0.1  and  0.04  per  cent  strength,  and  the  aeration  of  the 
cakes  so  essential  to  good  extraction  in  the  Homestake  ore.  The 
whole  operation,  exclusive  of  filling  and  emptying,  occupies  about 
six  hours.  At  the  time  of  my  visit  (January,  1907),  five  of  the  24 


CYANIDE  PRACTICE  AT  THE  HOMESTAKE       311 

presses  were  in  operation  and  working  most  satisfactorily;  the 
remaining  presses  were  partly  set  up  and  were  being  put  into  use 
as  fast  as  the  plates  arrived  from  the  factory.  Under  date  of 
Feburary  22,  Mr.  Merrill  writes  :  "We  are  now  treating  at  the 
rate  of  about  12,000  tons  per  month  and  will  increase  this  by 
several  thousand  tons  per  month  until  our  full  capacity  of  50,000 
tons  is  attained.  Cost  data  are  not  obtainable  yet,  but  will  not 
exceed  25c.  per  ton  for  all  items." 

Mr.   Merrill    submits  the  following  data    for  January,    1907; 

Tons  treated 7,670 

Assay-value   $0.85 

Recovery  in  precipitate 0 . 68 

Carried  over  -in  unprecipitated  solution 0 . 09 


Total  recovery  (equivalent  to  90  per  cent) .  .    $  0.77 
At  the  present  time  (May  1),  eleven  of  these  presses  are  work- 
ing continuously,  and  with  results  confirming  those  of  the  experi- 
mental plant  given  above. 

I  have  already  stated*  what  I  conceive  to  be  the  limitations  as 
well  as  the  merits  of  Mr  Merrill's  process.  In  all  fairness  it  may 
be  said  that  each  of  the  filtering  systems  now  in  vogue  possesses 
distinct  merits  of  its  own.  The  supreme  test  of  the  metallurgist 
in  these  days  of  many  inventions  is  to  select  the  right  process  for 
his  purposes,  that  is,  the  one  uniting  the  greatest  number  of 
advantages  when  applied  to  his  special  problem.  Of  Mr.  Merrill's 
system  it  may  be  said  finally  and  emphatically,  that  it  is  an  estab- 
lished success,  and  will  consequently  have  a  wide  range  of  use- 
fulness. As  for  the  installation  itself,  which  will  cost,  when  com- 
pleted, a  half-million  dollars,  I  question  whether  in  the  whole 
field  of  cyamdation,  we  shall  find  a  more  ingenious  and  original 
achievement,  or  one  more  conspicuously  uniting  metallurgical 
efficiency  with  perfection  of  mechanical  detail. 

*Mining  and  Scientific  Press,  December  15,  1906. 


VACUUM    SLIME     FILTERS 

(July  13,  1907) 

The  Editor  : 

Sir — In  view  of  the  articles  that  have  appeared  from  time  to 
time  in  the  columns  of  the  MINING  AND  SCIENTIFIC  PRESS  as  to 
the  merits  of  the  Moore  and  Butters  systems  of  vacuum-filters, 
having  had  some  experience  with  both,  I  would  like  to  add  a 
few  remarks  to  the  general  exchange  of  ideas  through  your  columns. 

I  do  not  think  there  is  much  difference  in  either  system  as 
far  as  cost  of  operation  and  maintenance  is  concerned,  but  I  do 
think  there  is  considerable  difference  when  "it  comes  to  the  main- 
tenance of  the  best  conditions  for  the  highest  efficiency  in  the 
vacuum  type  of  filter.  It  makes  no  difference  which  of  the  two 
filters  mentioned  is  used  for  making  the  cake,  as,  with  a  given 
vacuum  and  pulp  conditions,  either  of  them  makes  a  cake  equally 
fast.  Therefore,  it  comes  to  a  question  of  displacing  the  pregnant 
solution  contained  in  the  finished  cake  by  barren  solution  or  water. 

The  best  conditions  for  perfect  displacement  are  obtained  by 
having  a  homogeneous  mixture  of  the  pulp  in  the  filter-box  through- 
out the  time  of  making  the  cake  and  by  maintaining  uniform  con- 
ditions until  the  end  of  displacement,  when  the  deposited  slime 
is  ready  to  be  discharged.  By  uniform  conditions,  I  mean  a 
constant  vacuum,  constant  hydrostatic  pressure,  and  as  little 
exposure  to  the  air  as  possible.  Under  these  conditions  I  find 
that  the  displacement  is  almost  perfect,  no  appreciable  decrease 
in  strength  of  cyanide  being  noticeable  until  nearing  the  finish 
•of  displacement,  when  the  decrease  is  rapid  down  to  the  strength 
of  the  barren  solution  with  which  the  washing  is  being  done, 
which  shows  a  displacement  of  the  pregnant  solution  contained 
in  the  cake,  with  very  little  dilution. 

Dilution,  when  displacing  with  water  or  barren  solution,  is 
to  be  avoided,  as  it  means  a  larger  amount  of  solution  to  be  passed 
through  the  zinc-boxes,  and,  in  the  event  of  water  being  used, 
it  also  means  a  larger  quantity  of  waste  solution. 

The  methods  of  operation  of  both  the  Moore  and  Butters 
filters  have  been  given  at  some  length  in  your  columns  at  various 
times,  but  for  the  purpose  of  comparision  I  shall  briefly  outline 
them  again. 


VACUUM  SLIME  FILTERS.  313 

In  both  systems  the  storage,  or  equalizing- vat,  is  placed  to 
one  side  of  the  filter-box,  pulp  being  drawn  from  it  to  keep  the 
leaves  of  the  filter  submerged  during  the  formation  of  the  cake. 

In  the  Moore  system  the  whole  nest  of  leaves  (which  are  at- 
tached to  a  frame)  is  removed  from  the  filter-box  by  a  traveling 
crane  and  delivered  into  a  displacing- vat,  which  is  immediately 
alongside  the  filter- vat,  the  vacuum  being  maintained  during 
the  moving  of  the  loaded  nest  of  leaves  to  the  displacing- vats. 
The  unit  is  composed  of  three  filtering- vats,  two  for  displacing, 
and  one  in  the  centre  for  loading. 

When  the  crane  has  removed  the  filters  from  the  loading- 
vat  and  deposited  them  in  the  displacing-vat,  it  is  disconnected 
and  taken  to  the  other  nest  of  filters,  which  are  in  the  other  dis- 
placing-vat, and  when  the  slime-cake  on  the  filters  is  discharged 
they  are  brought  over  into  the  loading- vat,  and  the  making  of 
the  cake  commences  without  loss  of  time. 

In  the  Butters  system  the  filters  are  stationary  in  the  filter- 
vat,  and,  when  the  cake  is  made  the  pulp  is  pumped  back  into 
the  storage-vat,  the  vat  is  washed  out  with  solution  and  is  then 
filled  with  water  and  displacement  commences.  When  finished, 
the  cake  is  discharged,  the  surplus  water  is  run  back  to  storage, 
and  the  discharged  slime  is  sluiced  to  waste.  The  vat  is  again 
sluiced  out  to  remove  any  particles  of  the  discharged  cake  ad- 
hering to  the  sides,  and  again  pumped  full  of  slime  for  the  next 
cycle  of  operations. 

A  comparison  of  the  time  consumed  for  a  complete  cycle  is 
as  follows  : 


MOORE  SYSTEM  AT  LIBERTY  BELL  MILL,  TELLURIDE,  COLO., 
JANUARY,   1906. 

Hr.  Min. 

Making  cake 45 

Transferring  from  loading  to  displacing-vat  ....  5 

Displacing  or  washing  cake 1  0 

Sampling 

Discharging 15 

Transferring  from  displacing  to  loading-vat.   .  .  5 

Total  time  per  cycle -  >  •  *       2  15 


314  RECENT  CYANIDE  PRACTICE. 

BUTTERS  SYSTEM  AT  COMBINATION  MILL,  GOLDFIELD,  NEV., 
MARCH,   1907. 

Filling  filter-box  from  storage 25 

Making  cake 30 

Pumping  pulp  from  filter-vat  back  to  storage.  .  22 

Filling  filter-vat  with  waste  solution  or  water.  .  20 

Displacing  or  washing  cake 1          0 

Sampling 5 

Discharging 15 

Running  surplus  wash  solution  to  storage 6 

Sluicing  out  discharged  slime  residue 8 

Total  time  per  cycle 3       11 

In  comparing  the  above  tables  for  time  consumed  by  the 
various  steps  in  each  system,  it  will  be  noticed  that  the  transfer 
from  the  loading- vat  to  the  displacing- vat  in  the  Moore  system 
occupies  five  minutes.  During  this  short  period  of  time  the  va- 
cuum is  fully  maintained;  therefore,  there  is  no  change  in  this 
particular  part  of  the  operation;  the  exposure  to  the  atmosphere 
is  short  and  the  change  from  the  hydrostatic  pressure  of  the  pulp 
on  the  finished  cake  to  that  of  the  water  on  the  same  in  the  dis- 
placing-vat  is  rapid. 

In  the  Butters  system  the  transfer  of  the  remaining  pulp 
back  to  storage  after  the  cake  is  made  occupies  22  minutes; 
the  pumping  of  the  water  for  displacing  (after  all  the  pulp  is  out) 
occupies  20  minutes,  making  a  total  of  42  minutes  from  the  fin- 
ishing of  the  cake  before  displacement  can  be  commenced.  This 
long  period  necessitates  the  vacuum  being  dropped  from  21  to 
5  inches. 

The  difference  in  total  time  consumed  per  cycle,  other  than 
in  making  the  cake  and  displacing  it,  is  seen  to  be  30  minutes 
with  the  Moore  system,  and  1  hr.  41  min.  with  the  Butters,  the 
saving  in  favor  of  the  Moore  system  being  1  hr.  11  min.  per  cycle, 
but  the  saving  of  time  is  not  the  only  consideration. 

The  length  of  time  occupied  between  finishing  the  making 
of  the  cake  and  the  commencement  of  displacing  it  in  the  But- 
ters system  necessitates  dropping  the  vacuum  down  to  five  inches, 
or  barely  sufficient  to  hold  on  the  cake,  otherwise  the  cake  would 
be  so  badly  air-cracked  that  displacement  would  be  impossible. 


VACUUM  SLIME  FILTERS.  315 

(A  f-in.  cake  under  18  in.  vacuum  will  crack  beyond  redemption 
in  seven  minutes.) 

When  the  vacuum  is  lowered,  after  finishing  the  cake,  much 
of  the  moist  exterior  portion  of  the  cake  drops  off  when  the  hydro- 
static pressure  is  removed,  it  being  a  difficult  matter  to  adjust 
the  vacuum  at  the  best  point  for  any  particular  cake;  for  if  too 
high,  the  cake  will  be  badly  cracked  ;  and  if  too  low,  the  cake 
has  a  tendency  to  slough  off. 

In  the  42  min.  consumed  in  pumping  the  pulp  back  to  storage 
and  the  water  into  the  filter-box  for  displacement,  the  extreme 
top  of  the  cake  is  exposed  for  the  full  period  of  time  to  the  atmos- 
phere and  the  low  vacuum  that  is  maintained,  the  pulp  recedes 
slowly  down  the  cake  during  the  pumping  out  of  the  pulp,  and 
the  cake  is  slowly  submerged  during  the  entrance  of  the  water. 
Therefore,  there  is  a  period  of  time  (about  26  min.)  in  which  .the 
extreme  upper  half  of  the  cake  is  exposed  to  the  air  longer 
than  the  lower  half,  and  with  sufficient  vacuum  to  hold  the  cake 
on  the  filter-leaf  there  is  also  sufficient  to  cause  displacement  as 
the  water  slowly  rises  with  the  result  that  the  pregnant  solution 
in  the  lower  half  of  the  cake  is  thoroughly  displaced  long  before 
that  in  the  upper  half  and  a  large  amount  of  dilution  occurs,  as 
the  large  quantity  of  weak  barren  solution  necessary  for  displace- 
ment goes  to  prove,  at  the  Combination  plant  it  being  four  and 
one-half  times  the  amount  of  moisture  contained  in  the  cake 
before  displacement. 

It  will  be  seen  that  in  the  time  schedule  of  the  cycle  of  opera- 
tions the  Butters  system  will  have  to  be  considerably  changed  to 
allow  of  the  best  working  conditions.  And  I  consider  it  preferable 
to  use  one  vat  for  loading  and  a  separate  vat  for  displacing, 
as  then  the  small  loss  of  time  necessary  for  washing  out  the  filter- 
box  when  changing  from  pulp  to  water  and  the  reverse  are  avoided, 
and  it  also  avoids  the  constant  small  losses  that  are  bound  to  occur 
by  this  method  through  mixing  of  small  amounts  of  pulp  and 
pregnant  solution  with  waste  solution  when  they  go  through  the 
same  system  of  pumps  and  piping,  and  the  richer  the  solution 
the  greater  the  loss. 

The  wide  difference  in  the  capacity  of  the  two  plants  makes 
it  difficult  to  give  a  just  comparison  of  the  cost  of  operations, 
the  Liberty  Bell  plant  at  Telluride  having  a  capacity  of  450  tons 
per  day  and  the  Combination  Mines  plant  at  Goldfield  193  tons 
per  day  as  at  present  equipped. 


316  RECENT  CYANIDE -PRACTICE. 

The  labor  employed  at  the  Liberty  Bell  at  the  time  of  which 
I  write  was  two  men  on  each  shift,  one  of  whom  acted  as  shift- 
boss  and  had  general  supervision  of  settlers,  agitators,  and  Moore 
niters,  making  all  necessary  titrations  throughout  these  depart- 
ments. At  the  Combination  plant,  one  man  on  each  shift  attends 
to  the  filter-plant  besides  making  other  titrations  in  the  leaching- 
plant,  so  that  with  the  small  unit  as  installed,  that  is,  two  filter- 
boxes  of  28  and  30  leaves,  respectively,  one  man  per  shift  could 
possibly  handle  the  full  capacity  of  the  plant  or  193  tons  per  day. 

The  power  consumption  at  the  Liberty  Bell  is  two  10-h.p. 
motors  at  the  transferring  cranes  and  one  40-h.p.  motor  to  operate 
the  vacuum  and  other  auxiliary  pumps  connected  with  the  filter- 
ing system,  the  same  motor  also  operating  a  Goulds  triplex  pump 
that  returns  all  solution  used  in  milling  the  ore  to  the  top  of  the 
mill,  a  lift  of  about  80  ft.,  requiring  about  7  h.p.  constantly, 
the  total  power  consumption  being  53  h.p.  to  charge  against  the 
filter  equipment.  The  power  consumption  at  the  Combination 
plant  when  operating  two  Butters  pumps,  which  the  recent  new 
addition  makes  necessary  (the  plant  being  two  units) ,  is  20  horse- 
power. 

The  Combination  plant  then,  with  its  two  units,  one  of  28 
leaves  and  the  other  of  30  leaves,  can  handle  193  tons  of  dry 
slime  per  day  when  working  at  a  maximum  capacity,  with  labor 
of  one  man  per  shift  and  a  consumption  of  20  h.p.  The  Liberty 
Bell  plant,  with  its  four  sets  of  leaves  consisting  of  67  each,  will 
handle  450  tons  per  day  when  working  at  maximum  capacity, 
with  the  labor  of  two  men  per  shift  and  the  consumption  of  53 
h.p.  Therefore,  as  far  as  direct  comparison  of  the  actual  oper- 
ating costs  of  the  two  plants  goes,  there  is  not  much  difference. 
But  two  important  items  that  effect  the  capacity  of  the  Moore 
plant  at  the  Liberty  Bell,  and  that  so  far  have  not  been  taken 
into  consideration,  are  the  sticky  nature  of  the  ore  handled  and  a 
difference  of  3,000  ft.  greater  altitude. 

In  taking  up  the  question  of  maintenance  it  will  be  noticed 
that  the  total  number  of  leaves  in  the  Liberty  Bell  plant  is  268 
against  58  leaves  in  the  Combination  plant,  hence,  allowing  for 
an  equal  life  in  each  case,  the  renewal  cost  for  this  item  on  the 
Moore  plant  will  be  almost  five  times  as  great  as  on  the  Butters 
plant  at  the  Combination,  but  the  rule  previously  mentioned 
still  holding  good,  that  a  given  pulp  and  vacuum  condition  will 


VACUUM  SLIME  FILTERS.  317 

produce  the  same  cake  in  either  system,  the  Moore  plant  at  the 
Liberty  Bell  if  working  on  Combination  ore  would  have  a  capacity 
of  805  tons  per  day  against  193  tons  per  day  of  the  present 
Combination  plant.  In  the  moving  parts  of  the  crane  in  the 
Moore  system,  the  main  item  for  expenses  for  repairs  is  the  renewal 
of  the  lifting  cables,  which  require  renewing  about  once  a  year 
if  properly  adjusted  when  put  on.  The  repairs  that  are  necessi- 
tated by  the  cranes  are  offset  by  the  repairs  to  the  centrifugal 
pumps  in  the  Butters  system.  With  the  Moore  system,  where 
heavy  loads  of  slime  are  moved  from  one  vat  to  another,  there 
is  always  the  possibility  of  accidents,  for  instance,  a  cable  breaking 
and  causing  a  bad  wreck,  running  up  the  repair  bills  rapidly,  but 
with  properly  designed  apparatus  the  probability  of  such  an 
occurrence  is  very  remote. 

It  is  supposed  that  the  moving  of  the  niters  greatly  lessens 
their  life  by  straining  the  canvas;  such  is  not  the  case,  as  one 
cannot  feel  the  least  jar  when  the  crane  starts  to  lift,  the  vertical 
velocity  being  only  seven  to  eight  feet  per  minute  while  hoisting 
the  loaded  baskets  and  the  same  when  lowering  into  the  displac- 
ing-vat,  and  there  is  apparently  no  more  difference  in  the  cake 
or  filters  after  moving  than  if  they  had  not  been  removed  from 
the  loading-vat.  The  suspended  load  on  each  filter-leaf  is  the 
same  in  either  case,  whether  the  filter  with  its  load  of  slime  is 
removed  from  the  vat  full  of  pulp,  or  the  pulp  removed  from 
around  the  filter,  the  only  difference  being  in  the  length  of  time 
the  filter  is  required  to  sustain  the  load  of  slime,  unaided  by  hydro- 
static pressure  of  either  pulp  or  water,  which  maximum  length 
of  time  is  seen  to  be  five  minutes  in  the  Moore  system  to  44 
in  the  Butters. 

In  a  comparison  of  costs  of  installation,  a  58-leaf  plant  such 
as  is  used  in  the  Combination  mill  will  be  taken  and  the  main 
items  of  necessary  material  for  each  one  tabulated. 

BUTTERS   SYSTEM.  MOORE   SYSTEM. 

2     1  by  10  ft.  filter-boxes.  3  11  by  10  ft.  filter-boxes. 

1  14  by  12  ft.  pulp  storage-vat.  1  14  by  12  ft.  pulp  storage-vat. 

1  14  by  12  ft.  water       "  1  12  by  10  in.  vacuum  pump. 

1  12  by  10  in.  vacuum-pump.  1  10-h.p.  motor. 

2  4-in.  Butters  centrifugal  pumps.  1  20-ton  crane  equipped  with 
1  20-h.p.  motor.  1  10-h.p.  motor. 

58  filter-leaves.  1   4-in.  centrifugal  pump. 

58  filter-leaves. 


318  RECENT  CYANIDE  PRACTICE 

It  will  be  seen  that  the  Moore  system  requires  three  filter- 
boxes  against  only  two  needed  in  the  Butters,  only  one  storage- 
vat  being  needed,  and  that  for  pulp  in  the  first  instance,  as  against 
two  in  the  second  ;  and  a  20-h.p.  motor  against  two  10-h.p. 
The  main  difference  in  the  cost  of  installation  is  in  the  crane, 
which  will  add  35%  to  the  total  cost  of  the  plant.  The  above 
equipments  comprise  an  equal  filtering-area  in  each  case.  The 
Moore  system  will  handle  22  charges  in  12  hours,  and  the  Butters 
system  10  charges  in  12  hr.  44  minutes. 

To  summarize  :  The  operating  costs  of  either  system  are 
about  equal,  as  are  also  the  maintenance  and  repairs. 

The  installation  cost  for  the  Moore  system,  is  35%  greater 
than  the  Butters  system  for  an  equal  filtering- are  a. 

The  capacity  is  50%  greater  in  the  Moore  system  than  in 
the  Butters  system  for  an  equal  filtering-area. 

The  efficiency  of  the  Moore  system  for  the  recovery  of  preg- 
nant solution  with  the  least  amount  of  loss  and  dilution,  is  higher 
than  the  Butters  system  for  reasons  previously  given. 

There  is  no  doubt  but  that  given  ideal  topographical  con- 
ditions, the  Butters  system  can  be  a  great  deal  better  arranged 
than  here  at  the  Combination  plant. 

Where  sufficient  elevation  is  available  to  allow  of  ample  pulp 
and  water  storage  above  filter-boxes,  and  also  the  same  ample 
storage  below  (to  'again  allow  for  the  storage  of  pulp  and  water) , 
a  great  saving  of  time  is  obtainable  by  allowing  the  pulp  and 
water  to  flow  in  and  out  of  the  filter-box  rapidly.  This  would 
necessarily  greatly  increase  the  cost  of  installation.  Under  such 
conditions  the  amount  of  pulp  and  water  to  be  moved  back  up 
hill  after  each  cycle  of  operations  would  be  performed  over  a  long 
period  of  time  and  not  obstruct  the  filtering  operation,  instead 
of  a  short  period  during  which  filtering  operations  must  cease, 
as  at  the  Combination  plant. 

But  even  under  these  conditions,  which  have  materially 
lessened  the  time  consumed  and  also  improved  the  conditions 
for  displacement  by  removing  the  pulp  from  around  the  filters 
rapidly  and  getting  them  quickly  submerged  in  the  displacing 
medium,  we  have  not  eliminated  the  obvious  opportunities  for 
loss,  that  is,  by  alternately  running  pregnant  solution  and  water 
through  the  same  pumps  and  pipes  and  into  the  same  receptacles, 


VACUUM  SLIME  FILTERS.  319 

as  a  large  percentage  of  the  water  that  in  this  way  becomes 
mixed  with  the  small  amounts  of  pulp  and  pregnant  solution  has 
to  be  allowed  to  run  to  waste  with  the  discharged  cakes  of  slime. 
Therefore,  the  less  opportunity  there  is  for  any  such  mixing, 
whether  accidental  or  unavoidable,  the  better.  Hence  my  reason 
for  saying  that  a  loading-vat  in  which  the  cake  is  made  should 
be  used  for  that  purpose  alone.  And  the  same  reasoning  holds 
good  as  regards  pipe-lines  and  pumps  for  moving  pulp  containing 
pregnant  solution. 

Since  commencing  this  contribution,  Mr.  E.  H.  Nutter,  of 
the  Liberty  Bell  mill  at  Telluride,has  given  us  a  further  article  on  the 
Moore  niters  in  use  there,  slightly  changing  the  figures  as  shown 
in  the  table  I  have  given  for  time  consumed  per  cycle,  which 
change  no  doubt  comes  from  over  a  year's  further  experience  with 
the  plant.  I  am  hoping  that  he  will  furnish  us  with  some  val- 
uable figures  from  recent  operations  there,  and  that  Mr.  Mark 
R.  Lamb  will  do  the  same  with  reference  to  the  more  recent  install- 
ations of  the  Butters  system  in  Mexico,  for  the  benefit  of  the 
readers  of  the  MINING  AND  SCIENTIFIC  PRESS. 

A.  G.  KIRBY. 

Goldfield,  Nevada,  June  15. 


CONVEYING  TAILING  THROUGH  PIPE 

(July  20,  1907) 

The  Editor  : 

Sir — In  reply  to  your  request  for  further  data  concerning 
the  pipe-line  for  conveying  tailing,  mentioned  in  your  article 
appearing  in  the  issue  of  June  29,  I  beg  to  say  that  this  line  is 
5,440  ft.  long,  of  8-in.  cast-iron  bell  and  spigot  pipe,  f-in.  thick, 
and  joints  calked  with  hemp  rope  loosely  driven  into  place  after 
having  been  tarred.  It  is  laid  for  its  first  800  ft.  on  a  grade  of 
3J%,  after  which  it  has  a  uniform  grade  throughout  of  2J%. 
The  pipe-line  was  most  carefully  asphalted  on  the  specifications 
for  asphalting  pipe  contained  in  the  proceedings  of  the  Amer- 
ican Institute  of  Mining  Engineers  two  years  ago,  and  was  made 
by  the  American  Cast  Iron  Pipe  &  Foundry  Co.  at  Anniston, 
Alabama,  no  special  price  being  paid  for  said  asphalting,  which 
is  part  of  their  regular  practice,  apparently. 

The  line  of  pipe  passes  through  a  crowded  city  and  has  in 
its  construction  many  curves,  the  majority  of  which  are  on  a 
14-ft.  radius,  the  curves  being  made  by  short  sections  of  curved 
pipe  in  3-ft.  and  6-ft.  lengths,  ordered  for  that  purpose.  At  the 
head  of  this  line  are  two  de- watering  cones  of  20  ft.  diam.  with 
45°  sides;  these  remove  about  one-half  of  the  water  from  an 
eight  to  one  pulp  before  introduction  into  the  pump. 

The  pipe  was  put  into  service  at  the  middle  of  March,  1906, 
and  has  been  in  continuous  use  up  to  the  present  date,  having 
carried  approximately  100,000  tons  of  dry  pulp  during  that 
time.  Careful  measurements  of  the  interior  diameter  of  the  pipe, 
made  at  the  expiration  of  13  months  of  service,  show  that  it  has 
undergone  no  appreciable  wear.  The  total  cost  of  maintenance 
and  up-keep  during  the  13  months  has  been  3.57  pesos,  spent  for 
paint  on  one  of  the  viaduct  towers.  There  has  been  absolutely 
no  other  item  of  expense  since  its  installation. 

The  pulp  is  that  resulting  from  crushing  through  a  mill  of  80 
stamps  with  a  steel  wire  screen  of  26  mesh  with  28  wire  followed 
by  tube-milling  of  a  portion  of  the  coarse  product  such  that  after 
remaval  of  38%  of  the  pulp  as  slime,  52%  of  the  balance  nominally 
passes  a  120-mesh  screen.  At  times,  however,  when  the  tube-mill 


CONVEYING  TAILING  THROUGH  PIPE.  321 

has  been  out  of  service  for  replacement  of  linings,  we  have  run 
two  weeks  at  a  time  on  straight  26-mesh  battery -pulp.  On  two 
or  three  occasions,  by  reason  of  neglect  on  the  part  of  the  Mex- 
ican in  charge  of  the  de-watering  cones,  the  thickness  of  the  pulp 
has  been  considerably  increased  over  the  normal  four  to  one  propor- 
tion and  on  such  occasions  a  slight  deposit  of  coarse  sand  in  the  pipe 
has  occurred,  which  always  gives  notice  by  a  whistling  noise  at  a 
blow-hole  intentionally  placed  in  the  pipe  about  1,000  ft,  from 
its  head.  This. notice  always  occurs  in  plenty  of  time  for  the  error 
in  the  thickness  of  the  pulp  to  be  corrected;  on  two  occasions 
this  occurred  on  night-shift  and  the  line  filled  approximately 
half-full  with  coarse  sand,  but  an  hour's  time  was  sufficient  to 
clear  the  line  (by  the  introduction  of  more  water  at  the  head) 
with  no  expense  beyond  the  momentary  delay.  As  soon  as  riffles 
of  sand  are  formed  so  as  to  cause  an  obstruction  in  the  flow,  the 
pipe  develops  hydrostatic  head  above  the  point  of  obstruction 
sufficient  to  force  the  sand  through.  Delays  from  this  source 
have  not  caused  more  than  four  hours'  loss  of  time  in  the  entire 
13  months,  and  even  then  they  were  due  to  carelessness  at  the  cones, 
as  mentioned  above.  Normally,  month  after  month,  there  was 
not  the  slightest  tendency  of  the  pulp  to  deposit  any  sand  what- 
ever in  the  line  and  when,  due  to  electric  shut-downs  or  any  other 
stoppage  at  the  mill,  pulp  ceases  to  flow  into  the  head  of  the  pipe, 
the  line  keeps  itself  entirely  clear  without  the  introduction  of 
water. 

At  the  present  capacity  of  250  tons  per  day  the  pulp  runs 
only  If  in.  deep  on  the  bottom  of  the  8-in.  pipe,  running  at  such 
speed  that  the  distance  between  the  ends  of  the  line  is  traversed 
in  about  12  minutes.  The  additional  80  stamps  to  be  started 
in  September  will  double  the  amount  of  pulp,  but  the  pipe  can 
carry  1,000  tons  as  easily  as  the  present  250. 

The  wear  is  so  slight  as  to  be  invisible  up  to  date,  but  in 
any  case,  the  pulp  running  only  in  the  lower  part  of  the  pipe 
would  allow  of  the  turning  of  the  entire  line  five  times  before  it 
was  entirely  worn  out,  and  we  figure  that  if  the  line  were  to 
become  worn  out  every  two  years  it  would  only  mean  two  cents 
per  ton  carried.  The  present  appearance  is  that  it  will  last  50 
years. 

C.  W.  VAN  LAW. 

Guanajuato,  July  2. 


CYANIDATION     IN     THE     TRANSVAAL 

(July  20,  1907) 

The  Editor  : 

Sir — I  must  take  exception  to  your  Johannesburg  corre- 
spondent's remarks  in  your  issue  of  June  8.  Possibly  he  does  not 
understand  the  matter  he  criticizes;  otherwise  it  is  altogether 
difficult  to  understand  why  he  should  so  strongly  depreciate  the 
work  of  the  Denny  brothers  because  the  local  people  are  appar- 
ently unable  to  estimate  accurately  the  assay-value  of  their  ore. 

That  the, "new  metallurgy"  consisted  merely  of  a  method  of 
assaying  is  news  to  me.  What  the  Messrs.  Denny  announced 
was  that  : 

(a)  The  old  method  of  treating  coarse  sand  by  a  long  per- 
colation was  wrong  in  theory  and  in  practice  and  that  in  spite 
of  opposition  the  mines  would  abandon  it  in  favor  of  fine  grinding, 
for  which  purpose  they  introduced  tube-mills. 

(b)  By  the  use  of  tube-mills  they  expected  to  obtain  not 
only   a  higher  extraction  from  the  resulting  finer  grinding,  but 
also  a  higher  output. 

(c)  A    continuous   method    of   slime   treatment    by    having 
solution  occur  during  the  flow  or  travel  of  the  pulp  instead  of  in 
special   agitators   after    collection    and    settlement   was   cheaper, 
both    in   first    cost  of  plant  and  in   working,  than   the  prevalent 
decantation  method. 

In  order  further  to  increase  their  extraction  they  employed 
filter-presses  instead  of  decantation. 

All  their  points  the  Messrs.  Denny  appear  to  have  proved 
to  the  hilt.  Indeed,  the  use  of  tube-mills,  starting  from  the  one 
imported  by  the  Denny s,  has  now  spread  all  over  the  Rand;  and 
I  note  no  fault  whatever  is  found  with  the  extraction  obtained 
by  the  "new  metallurgy,"  and  that  in  the  same  speech  Mr.  Albu 
apparently  states  his  satisfaction  with  the  work  of  the  filter- 
presses.  His  one  cause  of  dissatisfaction  seems  to  be  his  difficulty 
in  obtaining  reliable  preliminary  assays  ;  but  this  surely  should 
not  be  insuperable,  and  is  an  entirely  subordinate  matter  to  the 
obtaining  of  the  highest  proportion  of  gold  at  the  minimum  cost 


CYANIDATION  IN  THE  TRANSVAAL.  323 

I  write  this  because  the  remarks  of  your  correspondent  are 
calculated  to  convey  a  wrong  impression,  and  not  because  I  am 
entirely  in  accord  with  the  line  taken  by  the  Dennys.  They  were 
cautious  in  their  preliminary  work  on  tube-mills  ;  their  verdict 
was  amply  justified  by  results.  They  did  a  good  deal  of  prelim- 
inary work  with  filter-presses  ;  there,  too,  their  decision  seems 
justified  by  results.  Whether  they  displayed  the  same  caution 
in  building  two  new  plants  depending  on  solution  of  the  gold  by 
what  we  may  term  'mortar-box  contact'  would  be  a  much  more 
debatable  subject  except  for  the  fact  that  it  appears  they  pro- 
vided additional  plant  for  the  purpose,  but  the  use  of  which 
was  not  found  in  practice  to  be  necessary,  and  I  have  been  advised 
— not  from  any  source  connected  with  the  Messrs.  Denny — that  Mr. 
Albu  has  strongly  objected  to  the  expenditure  of  the  money  on 
this  precautionary  measure,  though  the  vats_have  been  converted 
to  other  use. 

It  looks,  therefore,  not  merely  as  if  Messrs.  Denny  have  proved 
their  case  to  the  hilt,  but  that  indeed  this  same  system  has  been 
adopted  in  practically  all  the  latest  American  plants  and  in  a 
number  of  those  in  other  territories.  To  my  mind  a  serious  mat- 
ter against  the  new  system  is  the  difficulty  of  copper-plate  amal- 
gamation. In  Australia,  pans  are  successfully  used  for  the  purpose, 
and  I  have  no  doubt  that  other  suitable  methods  will  be 
devised  in  plenty — possibly  by  the  use  of  some  special  alloy  for 
amalgamating  plates — now  that  the  need  of  special  effort  in  this 
direction  is  known  ;  but  I  cannot  believe  that  a  method  of 
extracting  all  the  gold  in  the  slime  at  practically  no  expense  for 
plant  (as  far  as  the  solution  of  gold  is  concerned)  will  be  lightly 
abandoned  by  the  industry  (I  do  not  refer  here  to  South  Afri- 
can practice  only)  merely  because  of  a  faulty  or  ineffective  method 
of  obtaining  preliminary  assay-values.  The  saving  in  cost  of 
equipment  alone  is  a  factor  compelling  most  serious  attention. 

In  conclusion,  I  am  not  prepared  to  admit  that  the  Messrs. 
Denny  have  yet  made  made  out  their  case  in  favor  of  all-sliming. 
If  the  words  "finer  grinding"  are  substituted  for  "all-sliming" 
there  would  be  general  agreement  with  them,  but  personally  I 
am  of  opinion  that  it  is  still  the  most  satisfactory  and 
economical  method  in  general  practice — with  exceptions — to  per- 
colate in  vats,  without  expense  for  power  or  handling,  all  the  sand 
suitable  for  percolation  in  vats,  the  remaining  pulp  receiving  the 


324  RECE\7T  CYANIDE  PRACTICE 

suitable  treatment  necessary.  Apart  from  the  less  cost  of  thus 
creating  the  fine  sand,  we  have  as  yet  no  reliable  data  to  prove  that 
the  extraction  obtained  from  the  slimed  sand,  as  sand,  apart  from 
slimed  concentrate  or  slime,  is  so  much  higher  as  to  justify  the 
extra  cost  of  sliming  and  of  handling  the  slime.  There  may  be 
ores  in  which  total  sliming  is  preferable,  but  where  the  gold  is 
carried  in  the  concentrate  or  in  contact  with  some  softer  or  more 
fragile  material  it  is  surely  cheaper  to  treat  the  fine  particles  of 
sand  without  subjecting  them  to  the  partially  unrecovered  ex- 
pense of  further  grinding. 

ANOTHER  CORRESPONDENT. 
London,  June  26. 


CYANIDATION   IN  THE  TRANSVAAL 

(July  27,  1907) 

The  Editor  : 

Sir — We  have  read  in  your  issue  of  June  8  some  statements 
made  by  your  Johannesburg  correspondent  in  connection  with 
our  metallurgical  innovations  on  the  Rand  which  have  consider- 
ably astonished  us,  and  we  trust  that  as  you  have  circulated 
through  your  journal  statements  which  are  calculated  to  do  us 
some  harm  that  you  will  grant  us  the  use  of  your  columns  to 
rehabilitate  ourselves  in  the  eyes  of  your  readers. 

Your  correspondent  begins  by  stating  that  "several  of  the 
mines  under  our  control  spent  thousands  of  pounds  to  install  the 
process  of  circulating  cyanide  solutions  advocated  by  the  Denny 
brothers,"  and  follows  this  with  a  quotation  from  the  address 
of  the  Chairman  of  the  New  Goch  Co.  (on  which  mine  we  installed 
one  of  our  plants) ,  and  an  observation  of  his  own  that  the  Chair- 
man's statement  referred  to  "is  rather  disconcerting  to  the  'new 
metallurgy.'  ' 

Before  proceeding  to  deal  with  the  Chairman's  remarks  on 
the  subject  of  our  process,  we  would  like  to  point  out  that  not 
a  single  pound  was  spent  by  us  in  the  installation  of  the  process 
for  circulating  cyanide  solutions.  We  purposely  built  our  plants 
so  that  in  the  event  of  our  wishing  to  try  the  effect  of  circulating 
solutions  they  were  as  readily  adapted  for  that  as  for  our  ordinary 
treatment  without  circulating  cyanide  solution,  which  we  had 
installed  at  the  Van  Ryn  mine,  and  which,  we  may  add,  is  the 
system  to  which  it  is  proposed  now  to  revert  at  the  New  Goch. 
It  would  have  been  fair  to  us,  more  especially  as  we  are  not 
on  the  Witwatersrand,  to  reply  to  your  correspondent's  criticism, 
if  he  had  stated  that  after  all,  the  only  portion  of  the  plant  that 
the  Chairman  of  the  New  Goch  found  fault  with  was  the  system  of 
circulating  cyanide  solution,  and  that  the  main  principles  of 
our  plant,  embodying  tube-milling,  automatic  slime-treatment, 
and  filter-pressing,  remained  as  highly  successful  elements  of  the 
'new  metallurgy,'  and  constituting,  of  course  as  the  technical  man 
knows,  practically  the  whole  of  the  'new  metallurgy/ 


326  RECENT  CYANIDE  PRACTICE 

Coining  now  to  the  distinct  feature  of  our  system,  which 
has  been  pronounced  by  the  Chairman  of  the  New  Goch  to  have 
given  rise  to  difficulties,  we  would  observe  that  the  test  of  the 
efficiency  of  a  plant  is  high  extraction  coupled  with  low  working 
cost.  Neither  of  these  claims  are  questioned  by  the  Chairman, 
who  clearly  states  that  it  is  the  intention  to  abandon  the  circu- 
lating cyanide  solution  method,  merely  because  of  the  unreliable 
nature  of  the  screen-assays,  which  had  given  rise  to  erroneous 
estimates  of  the  gold  to  be  expected  at  the  monthly  clean-up. 

Adverting  first  to  the  efficiency  of  the  plant,  we  may  say, 
without  any  fear  of  contradiction,  that  the  residue  from  the  plant 
will  not  average  more  than  from  four  to  six  grains,  when  in  the 
former  plant  the  average  was  from  18  to  24  gr.  This  result  can- 
not be  said  to  be  unsatisfactory. 

The  assertion  of  the  Chairman  that  the  screen-assays  have 
proved  unreliable  is  one  we  can  neither  contradict  nor  confirm. 
In  our  complete  paper,  read  before  the  South  African  Association 
of  Engineers,  in  June,  1906,  we  admitted  the  difficulties  inherent 
in  the  practice  of  screen-sampling,  when  the  sample  itself  is  sub- 
jected to  the  solvent  effects  of  weak  cyanide  solution;  but 
we  also  pointed  out  very  emphatically  that  the  ordinary  system 
of  screen-sampling,  and  especially  the  usual  method  employed 
on  the  Rand,  were  open  to  even  graver  charges  of  contamination, 
which  charges  were  not  rebutted  in  the  ensuing  discussion. 

As  a  matter  of  fact,  we  might  mention  that  the  screen-assay 
at  the  New  Goch  during  several  years  of  our  experience  was  as 
unreliable  as  it  could  possibly  be,  and  we  attributed  it  then, 
and  now,  to  the  fact  that  the  ore  of  the  mine  contains  unusually 
coarse  particles  of  free  gold,  and  therefore  we  do  not  believe 
that  the  abandonment  of  the  circulating  solution  will  overcome 
the  difficulty,  while  we  are  certain  that  the  working  costs  will  be 
higher  and  the  extractions  lower.  We  make  the  last  statement 
quite  advisedly,  because  we  ran  the  plant  at  the  Meyer  &  Charl- 
ton  mine  (a  plant  the  exact  counterpart  of  the  New  Goch  plant), 
first  without  cyanide  solution,  and  carefully  noted  the  results; 
and  subsequently  with  cyanide  solution  in  circulation,  thus  getting 
actual  working  figures  for  comparison.  The  important  differ- 
ences are  given  in  our  paper  previously  referred  to. 

What  is  the  more  inexplicable  part  of  this  change-over  on 
the  New  Goch  mine,  is  that  with  an  exactly  similar  plant  at  the 


CYANIDATION  IN  THE  TRANSVAAL.  327 

Meyer  &  Charlton,  extraordinary  success  has  been  attained; 
which  is  attested  by  the  fact  that  the  manager  of  the  mine,  when 
showing  the  members  of  a  scientific  society  over  the  plant  at 
the  end  of  last  year,  stated  that  the  extraction  up  to  that  date, 
nearly  a  year  after  the  plant  had  started  running,  was  95%.  We 
may  mention  that  with  the  former  plant,  our  extractions  averaged 
.between  80  and  85%  only,  so  that  the  new  plant,  according  to 
the  official  statement  of  the  manager,  is  responsible  for  10% 
higher  extraction,  at  an  increased  working  cost  of  one  shilling 
per  ton;  the  net  result  being  from  4  to  5s.  per  ton  profit  in  favor 
of  the  new  plant.  Our  estimate  on  which  the  plant  was  built 
was  a  net  improvement  of  4s.  per  ton  in  the  profits. 

It  is  interesting  to  observe  that  the  Chairman  of  the  New 
Goch,  wrho  is  also  Chairman  of  the  Meyer  &  Charlton,  stated  in 
his  annual  address  in  1907,  when  dealing  with  the  operations  for 
the  past  year,  that  "the  larger  profits  resulting  (from  the  year's 
work)  have  more  than  justified  the  expenditure  occurred  in  the 
additions  to,  and  improvement  of,  the  plant."  He  further  stated 
that  "the  company  had  produced  more  gold  and  earned  a  larger 
profit  than  in  any  previous  year,"  the  actual  figures  being  with 
the  old  plant  for  1905  a  gross  profit  of  £99,784,  and  with  the  new 
for  the  year  1906  a  gross  profit  of  £136,967,  or  an  increase  of 
over  36  per  cent. 

The  question  now  arises  why,  with  the  Meyer  &  Charlton 
plant,  such  magnificent  results  have  been  secured,  and  why  at 
the  New  Goch  they  have  been  so  disappointing  as  to  give  rise 
to  the  criticisms  and  damning  statements  of  your  correspondent. 

We  are  in  position  to  say  that  during  the  time  we  were 
in  control  of  the  plants,  we  made  complete  clean-ups  of  the  new 
Meyer  &  Charlton  plant,  first,  to  satisfy  ourselves  that  the  gold 
called  for,  as  between  the  screen  assays  and  the  residue-assays, 
was  in  the  plant,  and  subsequently,  at  the  instance  of  the  Chair- 
man of  the  company,  on  more  than  one  occasion,  to  satisfy  his 
doubt  on  the  matter.  The  clean-up  was  in  each  case  a  com- 
plete vindication  of  our  methods,  as  we  had  in  each  case  a  plus 
extraction.  In  the  face  of  these  results,  and  of  the  actual  record 
of  the  Meyer  &  Charlton  with  its  new  plant,  for  1906,  we  think 
that  you  must  agree  that  your  correspondent's  strictures,  and 
his  concluding  observation  that  "it  is  fortunate  for  the  rest  of 
the  Rand  that  conservative  counsels  prevailed,  and  that  the 


328  RECENT  CYANIDE  PRACTICE 

mines  of  other  groups  did  not  take  up  the  metalliferous  schemes  so 
persistently  promulgated  by  the  Messrs,  Denny,"  are  unfair.  It  is 
rather  unfortunate  for  your  correspondent  that  this  final  statement 
should,  in  any  case,  so  inaccurately  represent  the  actual  situation. 

We  were  solely  responsible  for  the  introduction  of  tube-mills, 
and  the  leading,  if  not  the  only,  advocates  for  fine-grinding,  and 
secondary  amalgamation.  Our  principles  have  been  accepted 
and  a  plant  to  carry  them  out  has  been  installed  on  every  up-to- 
date  mine  on  the  fields.  We  are  again  solely  responsible  for 
the  introduction  of  filter-presses  to  the  Rand.  Slowly,  but  surely, 
these  appliances  are  being  installed,  and  no  less  than  five  big 
mines  are  at  the  moment  putting  them  in.  We  are  solely  respon- 
sible for  the  introduction  to  the  Rand  of  a  new  form  of  mortar- 
box,  in  which  the  water-feed  is  delivered  through  the  back  of  the 
box,  at  about  the  level  of  the  die.  We  learn  from  the  consulting 
metallurgist  to  the  leading  group  on  the  field,  that  the  same 
method  has  been  adopted  by  them  with  the  greatest  success. 

In  conclusion,  we  would  say  that  when  the  whole  cause  of 
dissatisfaction  with  our  plant  is  boiled  down  it  merely  refers  to 
the  fact  that  on  a  particular  mine,  disappointments  in  the  gold 
yield  have  been  experienced,  which  on  that  particular  mine  is 
no  new  thing.  We  assert  without  any  fear  of  contradiction, 
that  the  only  other  mine  on  which  we  installed  a  plant,  where 
the  dissappointments  indicated  have  never  existed,  a  complete 
clean-up  of  the  plant  has  always  shown  rather  more  gold  than 
the  screen-assay  called  for.  The  reversion  to  the  so-called  de- 
cantation  system,  about  which  the  Chairman  of  the  New  Goch 
and  your  correspondent  have  both  made  so  much,  does  not  in- 
validate one  single  principle  of  our  scheme,  nor  cause  the  slight- 
est alteration  to  our  plants,  other  than  the  substitution  of  water  for 
weak  cyanide  solution,  and  a  dam  for  receiving  the  slime  and 
solution  from  our  specially  designed  slime-plants,  which  latter, 
as  a  matter  of  fact,  we  provided  before  the  plant  was  started. 

The  whole  of  the  details  of  this  scheme  we  worked  out,  and 
successfully  practised  at  the  Van  Ryn  mine,  with  an  equipment 
of  160  stamps.  We  are  sorry  that  an  explanation  of  the  true 
position  in  connection  with  our  plant  *has  necessitated  so  much 
space,  but  we  believe  it  to  be  due  to  our  friends  arid  ourselves 
to  state  the  position  fully  and  clearly.  DENNY  BROS., 

London,  June  27.  Per  G.  A.   DENNY. 


TUBE-MILLS  AT  GUANAJUATO 

(August  17,   1907)J 

The  Editor: 

Sir — As  to  our  experience  with  our  tubes:  Apparently  it 
has  been  markedly  different  from  that  of  a  good  many  people, 
and  we  really  do  not  understand  the  reason  why,  as  we  have 
had  no  difficulty  whatsoever,  aside  from  routine  replacements  in 
the  eight  or  nine  months  we  have  been  running  them.  These 
mills,  as  you  know,  are  the  Abbe  mills,  4  ft.  6  in.  by  20  ft.,  and  are 
handling  about  80  tons  of  pulp  per  day. 

A  screen  test  made  on  pulp  going  to  the  tube-mill  shows: 

• 

Mesh.  Per  Cent. 

Remaining  on     40 11.2 

50 11.2 

60 8.9 

80 16.6 

100 16.3 

120 26.1 

Passing                120 9.7 

Moisture  60  per  cent. 

The  screen  test  on  discharge-pulp  shows: 

Mesh.                                                                                        Per  Cent. 

Remaining  on     40 0.5 

50 1.7 

60 2.9 

80 6.0 

100 16.2 

120 21.8 

Passing                120 51.2 

Mechanically  the  mills  have  given  us  no  trouble  since  their 
installation,  with  the  exception  that  the  first  pinion  shipped  with 
the  mills  was  shrouded  and  the  distance  between  the  shrouds  was 
not  sufficient  to  allow  for  any  end  motion  whatsoever  of  the  mill 
as  a  whole,  and  the  gear  ultimately  rode  the  shroud  of  the  pinion, 
smashing  both  the  gear  and  the  pinion,  but  doing  no  further 
damage;  since  replacing  with  a  pinion  wider  between  the  shrouds, 
no  difficulty  whatever  has  been  had. 

To  limit  the  end  motion  upon  this  type  of  mill,  two  guide- 
rollers  with  vertical  axis  bear  upon  the  sides  of  the  supporting 
tire  next  the  gear  end,  and  a  good  deal  of  trouble  has  been  had 
by  earlier  users  of  the  mill,  we  understand,  on  account  of  the  ten- 


330  RECENT  CYANIDE  PRACTICE. 

dency  of  the  mill  to  run  endwise,  being  so  severe  that  these  guide- 
rollers  were  quickly  worn  out;  the  Abbe  Company  suggested  to  us, 
before  our  first  mill  was  installed,  that  it  was  possible  to  cant  the 
friction-rollers  upon  which  the  tire  moves  (and  which  constitute 
the  support  of  the  mill)  in  such  a  way  as  to  cause  the  main  tube 
to  go  in  either  direction  longitudinally,  and  that  by  delicate 
adjustment  of  this  canting,  it  should  be  possible  to  confine  the  mill 
entirely  to  one  position  without  its  bearing  unduly  hard  on  either 
of  the  guide  rollers.  We  experimented  with  this  and  within 
the  first  day  or  two  after  the  mill  was  started  we  found  it  possible 
by  this  adjustment  to  cause  the  main  tube  to  'float'  entirely  free 
on  its  supporting  rollers  without  touching  either  of  the  guide- 
rollers  at  alj,  and  the  mill  ran  for  three  months  at  one  time  without 
touching  either  guide-roller,  and  normally  it  hardly  touches  them 
once  a  day. 

The  silex  lining  of  the  mills  has  given  good  satisfaction,  the 
first  lining  running  eight  months  before  it  had  to  be  replaced, 
though  at  the  end  of  about  six  months,  three  or  four  defective 
blocks  were  replaced,  with  a  two  days'  shut-down. 

A  great  deal  depends  apparently  upon  the  truth  of  the  sup- 
porting tires  and  the  homogeneity  of  the  material  composing  it, 
because  if  in  these  tires  the  slightest  irregularity  occurs,  either 
as  an  original  defect  or  as  the  result  of  operation,  bumping  would 
rapidly  ensue,  which  would  cause  the  destruction  of  the  mill  and 
perhaps  its  foundations.  So  true  is  this  that  we  found  on  starting 
the  first  mill,  that  a  film  of  Vie  °f  an  mc^  °f  sand,  which  had  accu- 
mulated on  certain  oily  spots  on  the  tire,  caused  violent  bumping, 
until  the  mill  was  stopped  and  the  ring  tire  carefully  cleaned  off. 
We  keep  these  tires  at  all  times  carefully  cleaned  and  a  little  oil 
is  put  on  the  surface  of  the  tire  once  or  twice  a  day.  Since  the 
tires  were  first  cleaned,  there  has  not  been  the  faintest  bump 
or  vibration  evident  about  either  mill,  the  mills  running  as  quietly 
and  smoothly  as  possible.  The  mills  are  kept  filled  slightly  above 
centre  with  pebbles,  the  pebble  wear  being  approximately  f  Ib. 
per  ton  of  ore  treated ;  silex  linings  wear  eight  months ;  power  to 
start  the  mill,  about  60  h.p.,  which  immediately  drops  to  43  h.p. 
as  soon  as  at  running  speed. 

Trusting  that  the  above  data  may  be  of  interest  to  some  of 

your  readers. 

~  TVT     •       T  1  C.  W.  VAN  LAW. 

Guanajuato,  Mexico,  July  14. 


CONVEYING  TAILING   IN  LAUNDERS 

(September     14,   1907) 

The  Editor: 

Sir — -I  have  read  with  much  interest  the  description  appear- 
ing in  your  issue  of  June  29,  on  conveying  tailing  in  cast-iron  pipe 
at  Guanajuato,  also  the  further  statements  on  the  same  subject 
by  Mr.  Van  Law  in  the  issue  of  July  20.  Having  in  the  last  two 
years  made  about  7,000  experiments  on  the  carrying  capacity 
of  launders,  the  subject  is  of  course  interesting  to  me.  In  my 
experiments  on  tailings  which  were  clean  pure  quartz  and  quartzite 
(probably  much  more  angular  and  sharp  than  the  material 
at  Guanajuato)  I  find  that  on  a  grade  of  1.5%  in  a  rectangular 
launder  on  material  of  the  fineness  mentioned  in  your  article  one 
pound  of  water  will  only  carry  off  0.022  Ib.  quartz,  when  the  launder 
has  the  most  economical  width  for  the  quantity  of  material  carried. 

My  experiments  also  show  that  with  the  most  economical 
width  of  launder,  the  same  material  with  water  in  the  proportion 
of  7J  to  1  would  require  a  grade  of  nearly  5%.  Only  on  absolute 
slime  did  I  obtain  better  results  in  a  V-shaped  launder  than  in  a 
rectangular  one.  My  experiments  were  checked,  some  twice 
and  some  three  times. 

Why  my  results  are  so  much  lower  than  those  mentioned, 
I  would  like  to  ascertain.  I  know  Mr.  Van  Law  personally  and 
know  the  figures  he  has  given  can  be  nothing  but  correct,  and  the 
difference  must  be  wholly  in  the  nature  of  the  two  materials  han- 
dled (this  refers  to  the  issue  of  June  29). 

With  your  permission,  and  begging  the  pardon  of  my  brother 
engineers,  I  can  positively  state  that  the  "wetted  perimeter"  has 
nothing  whatsoever  to  do  with  the  carrying  capacity  (as  far  as 
solids  go)  of  a  launder.  Personally,  I  was  formerly  under  the 
impression  that  it  had,  but  my  experiments  have  conclusively 
proved  that  we  have  all  been  wrong  in  this  assumption.  For 
example,  a  1-in.  launder  using  25  Ib.  water  per  min.  will  carry 
exactly  one-half  of  the  tailing  of  a  2-in.  launder  using  50  Ib.  water, 
and  one-tenth  of  a  10-in.  launder  using  250  Ib.  water  per  min., 
all,  of  course,  on  the  same  grade;  that  is,  the  carrying  capacity 
in  sand,  etc.,  is  proportional  to  the  width.  This  I  can  prove 
by  figures  from  about  500  actual  experiments.  In  the  next,  state- 


332  RECENT  CYANIDE  PRACTICE 

ment  I  shall  probably  get  myself  into  trouble,  but  Mr.  Van  Law's 
experience  will  bear  me  out. 

Under  the  right  conditions,  material  can  be  transported  in 
a  pipe.     On  a  grade,  we  could  not  possibly  transport  it  in  an  open 
launder,  but  the  initial  grade  should  be  greater  than  the  grade 
at  the  end  (the  sooner  to  develop  pressure)  which  in  an  open  launder 
would  be  bad  practice.     But,  as  a  rule,  we  can  only  utilize  a  pipe 
on  very   fine  material,   and  when  'handling  comparatively   large 
quantities.     To  make  myself  clear,   if  we   attempt  to  transport 
in  a  pipe  J-in.  material  at  the  rate  of  10  Ib.  per  min.  on  a  certain 
grade,  with  the  least  quantity  of  water,  the  theoretical  size  of  pipe 
required  would  be  so  small  that  in  a  short  time  the  pipe  would  clog, 
but  to  transport  100-mesh  material  through  the  same  pipe  would 
be  easy.    I  know  full  well  that  pipes  used  in  mills  in  place  of  launders, 
often  give  much  trouble  and  it  is  not  my  purpose  to  recommend  pipe 
in  place  of  launders,  except  for  carrying  off  great  quantities  of 
comparatively    fine    tailing.     There   is    more    to    Mr.    Van    Law's 
expression,  which  I  will  quote,  than  most  of  us  (probably  even  him- 
self included)  would  think.     "As  soon  as  rifHes  of  sand  are  formed 
so  as  to  cause  an  obstruction  in  the  flow,  the  pipe  develops  hydro- 
static head  above  the  point  of  obstruction  sufficient  to  force  the 
sand  through."     That  is,  if  the  pipe  is  too  large  to  give  the  velocity 
of  water  that  will  keep  the  material  in  suspension   (or  carry  it 
on  the  grade  used)   then  nature  itself,  by  the  filling  in  of  sand, 
reduces  the  size  of  the  pipe  down  to  the  point  where  the  velocity 
will  be  high  enough  to  carry  the  material  off,  depositing  it  ahead 
again  where  velocity  is  slower,  until  this  point  in  turn  reaches  the 
carrying  stage,  and  so  on.     This  action  also  shows  to  some  extent 
in  a  launder,  but  the  effect  is  not  the  same  as  in  a  pipe,  because 
the  launder  can  keep  on  filling  up  and  water  still  flows  on  top, 
without  increasing  its   velocity   at  that  point.     The   carrying  of 
tailing  in  a  pipe  and  in  a  launder  are  two  entirely  different  problems , 
and  do  not  at  all  follow  the  same  laws.     In  the  pipe  we  depend 
mostly  on  the  head  developed,  but  in  the  launder  on  the  rolling^ 
and  sliding  action  down  an  inclined  plane,  except  in  the  case  of 
exceedingly  fine  material,  where  the  hydraulic  condition  or  wetted 
perimeter  approximates  the  right  proportion  of  a  launder.     I  hope 
in  another  year  to  finish  my  investigation  in  regard  to  the  problem 
of  launder  capacity  and  to  present  it  in  much  better  form  than  these 
ramblings.  ~     .     ~ 

«    ,f  T     ,       ,*..          A  G.  A.   OVERSTROM. 

Salt  Lake  City,  August  31. 


CONVEYING  TAILING  IN  LAUNDERS 

(October  12,  1907) 

The  Editor: 

Sir — The  courteous  query  for  more  light  in  your  issue  of 
September  14,  and  signed  by  Mr.  G.  A.  Overstrom,  deserves  full 
data  in  answer. 

The  conditions  are  not  quite  as  Mr.  Overstrom  takes  them. 
The  ore  crushed  is  an  exceeding  hard  tough  quartz,  with  very  small 
admixture  of  calcite,  and  no  other  gangue ;  it  is  therefore  very  sharp 
and  granular.  The  coarser  portion  of  the  pulp  which  results 
from  battery  crushing  through  26  mesh  28  wire  steel  screens  is 
tube-milled,  and  the  resulting  screen-test  after  tube-milling 
is  as  follows: 

PULP  WHEN  USING  TUBE-MILLS 


Remaining  or 
Passing 

Mesh, 
i     40  

Per  Cent. 
..31 

50  

4.4 

60  

2.8 

80 

4  1 

100 

4  3 

120 

10  0 

150      

3.1 

150.  . 

.   68.2 

The  line  has  for  several  weeks  at  a  time,  however,  been  run 
without  the  tube-mills  running,  therefore  taking  the  straight 
battery  product,  screen  test  of  which  is  as  follows: 


Remaining  or 
Passing 

STRAIGHT  BATTERY  PULP 
Mesh, 
i     40                       .    .                     

Per  Cent. 
5.1 

50  

5.2 

60 

52 

80 

5.7 

100 

.  .      5.6 

120 

11.8 

150 

1.7 

150.  . 

.    59.7 

The  normal  proportion  of  water  that  these  pulps  contain 
in  the  pipe-line  is  about  five  to  one  by  weight,  and  while  there 
is  no  doubt  that  the  hydrostatic  head  formed  behind  riffles  of  sand 
in  the  pipe  when  such  occur  greatly  assists  in  preventing  the  com- 
plete clogging  of  the  pipe,  this  action  has  only  occurred  a  few 


334  RECENT  CYANIDE  PRACTICE 

times  in  the  eighteen  months  that  the  pipe  has  been  running,  and 
normally  has  no  influence  whatsoever.  Under  normal  conditions, 
embracing  all  but  a  few  hours  since  the  line  was  installed,  there 
are  no  riffles  whatsoever  in  the  line  and  the  upper  three-quarters 
of  the  pipe  is  entirely  clear,  the  pulp  flowing  in  a  smooth  rapid 
stream  without  ripples  or  disturbance  in  the  lower  quarter  of  the 
pipe,  precisely  as  in  an  open  launder.  I  may  say  that  since 
adding  the  second  80  stamps,  the  line  which  now  carries  pulp 
from  160  stamps  is  running  slightly  less  than  half  full, 

Mr.  Overs trom's  difficulty  in  reconciling  the  performance 
with  many  detailed  experiments  is  shared  by  many.  During  the 
time  of  installation  of  the  line  the  number  of  expert  opinions 
passed  upon  whether  it  would  run  or  not  and  based  upon  experi- 
ences' with  launders,  was  very  large  and  with  one  solitary  excep- 
tion, flatly  unfavorable.  We  had,  however,  demonstrated  experi- 
mentally that  pulp  much  thicker  than  that  now  being  handled 
and  somewhat  coarser,  would  run  freely  in  an  identical  pipe-line 
300  ft.  long  on  a  2J%  grade — running  so  freely,  in  fact,  that  we 
felt  justified  in  going  to  a  2J%  grade  to  better  fit  the  contour  of 
the  country. 

The  limitations  of  the  line  seem  clearly  marked.  With  the 
tube-mills  running,  no  tendency  to  clog  has  ever  been  discovered. 
With  the  tube-mills  out  and  on  straight  battery  pulp  if  the  water 
is  reduced  to  less  than  five  to  one,  riffles  of  sand  commence  to  form 
at  a  point  about  500  ft.  from  the  upper  end  of  the  line,  giving 
notice  there  by  a  whistling  .noise,  due  to  the  air  disturbance  in 
the  pipe,  which  issues  through  a  blow-hole  placed  at  that  point. 
The  restoration  of  the  proper  dilution  at  the  thickening  cone 
at  once  corrects  the  fault. 

..'  The  economic  importance  of  being  able  to  transfer  tailing 
over  great  distance  at  such  small  grades  and  at  practically  no 
cost  (as  evidenced  in  our  expense  of  P3.57  as  the  total  charges 
against  the  carrying  of  100,000  tons  of  ore  a  mile  in  distance)  is 
considerable,  hence  the  intrusion  upon  your  space  with  the  fore- 
going detail. 

The  wear  upon  the  line  to  date  is  not  measurable  after  eighteen 
months'  service. 

C.  W.  VAN  LAW. 

Guanajuato,  September  28. 


INDEX 


Page 

Absorption  of  Metals 41 

Amalgamation 61,  74 

83,  93,  142,  201 

Arents,  Albert 45 

Arents,  C.  A 132 

Assay  of  Cyanide  Solution.  .  .  42  50 
240,  251,  267 

Banks,  E.  G ... 253 

Barry,  H.  P 67,238 

Beilby.  G.  T.  ....... 9 

Blaisdell  Apparatus 27 

Boss,  M.  Pi.  . 31,  154 

Bosqui,  .Francis  L 25,  33, 

39,  51,83,  136,  172,  181,302 

Bradley,  W alter  W .' .    207 

Brett,  H.  T 189 

Brown,  R.  Gilman 92,  98,  157 

Bryan    Mills 143 

Bullock,  L.  N,  B 231,  265 

Burt,  Edwin 117,  234 

Butters,  Charles 55,  82,  204 

Butters  Filter 147,  1 78, 

185,  213,  218,  227,  235,  241,  269,  312 

Caetani,  G 117 

Cassel,  H.  R 47 

Chandler,  E.  D 161 

Chiddey,  Alfred 42 

Chilean  Mills 37 

Chlorination 139 

Clarke,  Robert 245 

Clean-up 89,210 

Coarse  Gold 84 

Combination  Mill 34,  52,  136 

Concentrate,  Cyanidation  of . .  22,  107 

Concentration 202 

Consumption  of  Cyanide 11 

Conveying  Tailing  by  Pipe  .297,  320, 

331,333 

Copper,  in  Cyanide  Solution.. 90,  132, 

161 
Cost. 

Bodie 106 

Filtering 19 

Filters 179 

Goldfield 150,  152,  183 

Guanajuato 260 

Homestake 187,  306 

Melting  Precipitate 164 

New  Zealand 69 

Rand 63 

Western  Australia 205 

Crosse,.A 45 

Crushing 197 


Page 
Crushing  and  Grinding  Practice 

at  Kalgoorlie 73 

Cyanidation  at  Copala 231 

Cyanidation  of  Concentrate.  .22,  107 

Cyanide  Notes 86 

Cyanide  Practice. 

Bodie 92 

Copala 231,265 

Cripple  Creek 17 

El  Oro,  Mexico 55,  114,  125 

Factor  in  Gold  Production. . .        9 

Guanajuato 12,  22,  254,  296 

Homestake 80,  172,  186,  302 

Kalgoorlie 73,  189 

Korea 110,  262 

Mercur.,  .  .  . 93 

Nevada 25,33,51,82,  136,269 

Salvador 164 

South  Africa.59,  200,  210,  267,  322, 

325 

Waihi  Mine 69,  253 

Western  Australia 17 

Cyanide  Poisoning 123 

Cyanide  Solution,  Copper  in. . .  .    90, 

132,  161 

Dehydration 93 

Denny,  G.  A.  and  H.  S 59  267 

322,  325 

Desert  Ores,  Treatment  of.  .  .  51,  65, 

82,  247 

Diehl  Process 20,  73 

Direct  Treatment 82 

Doveton,  Godfrey 16 

Drucker,  A.  E 110,  166,  262 

Durant,  H.  L 46 

Esperanza  Mill 130 

Extraction 53,  61,  64,  82, 

89,  105,  113,  129,  131,  138,  255,  257 

Filtering  Cost. 19 

Filter-Press  Practice.  .  18,  27.  61,  92, 

98    147,   153,   174,  182,  213,  218, 

221,  227,  235,  241,  249,  269,  312 

Fine. Grinding 16,  25, 

29,31,37,73,94,  198,257 

Gartrell,  H.  W 153 

Gendar,  H.  W 241 

Grinding,  Fine 16,  25, 

29,  31,  37,  73,  94,  198,  257 
Guanajuato,  Cyanidation  at..  12,  22, 

254,  296 

Hamilton,  E.  M 12,  164,  254,  269 

Hobson,  Francis  J 12,  22 

Homestake  Mill 302 


INDEX 


Hunt,  Bertram 65,  247 

Huntington  Mills 130 

Iron  v.  Wood 39 

James,  Alfred 67,  72,  195,  196 

Julian,  H 155 

Kessler,  H.  H 176 

King,  Lochiel  M 82 

Kirby,  A.  G 312 

Lamb,  Mark  R 134,  213,  218,  241 

Launders  for  Conveying  Tailing  331, 

333 

Leaching  Vats. 39 

Lime 119,309 

Lining  of  Tube-Mills. 56,  69, 

95,  121,  162,  166,  174,  199,  207.  238 

MacDonald,  Augustus 267 

MacDonald,  Bernard 255 

McMiken,  S.  D 162 

Magenau,  Wm 42 

Melting  Precipitate   164,  264 

Mercuric  Cyanide 205 

Merrill,  C.  W 172,  304 

Metallurgical  Development  on 

the  Rand 59 

Mexican   Gold    and    Silver    Re- 
covery Company 12 

Meyer  &  Charlton  Mill 60,  327 

Mill. 

Combination 34,  52,  136 

Esperanza 130 

Homestake 302 

Meyer  &  Charlton 60,  327 

Standard 92 

Miller,  Grant  D 45 

Milling  v.  Smelting 33 

Mills. 

Bryan 143 

Chilean 37 

Huntington 130 

Mitchell,  D.  P 78 

Moore  Filter 92,  98, 

174,  184,213,312 

Muir,  Douglas 251 

Nutter,  E.  A 170,  174 

Overstrom,  G.  A 331 

Oxygen  in  Cyanide  Solution..  .      155 

Pans  for  Grinding 31,  78, 

107,  191,245 

Pans  v.  Tubes 78 

Parsons,  A.  R 227 

Percolation 107 

Pettis,  E.  S 235 

Pipe  for  Conveying  Tailing .  297,  320, 

331.333 


Page  Page 

Precipitation. 80,  89, 

126,  132,  134,  310 

Progress  in  Cyanidation 67   172 

Rickard,  T.  A 114,  125,  254,  296 

Ridgway  Filter 221 

Roasting 201 

Sampling  Tailing 157 

Sand  Index 127 

Settlement  of  Slime 270 

Settling  Vats 97 

Siphon  for  Removing  Floating 

Material 215 

Slime  Denned 29,  154 

Slime  Filter 249,  252 

Slime  Treatment 16,  26, 

118,  249,  258,  299,  203,  306 
Solution 

Assay  of 240,  251,  267 

Copper  in 90,  132,  161 

Meter 170 

Oxygen  in.. 155 

Strength  of 89,  111,  126  145 

Standard  Mill.  .  .' 92 

Stevens,  F.  B 48 

Stines,  Norman  C 50 

Strength  of  Solutions 89,  111, 

126,  145 
Sulphide  Ore,  Treatment  of.  ...    148 

Tailing  Samplers 157 

Tays,  E.  A.  H 86 

Thomas,  James  E 210 

Treatment  of  Desert  Ores..  .  .  51,  65, 

82,  247 

Treatment  of  Slime 16,  26, 

118,  249,  258,  299,  203.  306 

Treatment  of  Vat 262 

Tube-Mills. 

California 94,  175 

Colorado 175 

Kalgoorlie 78,  191 

Korea 110 

Lining  of 56,  69, 

95,  121,  162,  166,  174,  199,  207,  238 

Mexico 55,  120,245,329 

Nevada 149 

On  the  Rand 59  328 

Pebbles 58 

Van  Law,  Carlos  W 297,  320, 

329,  333 

Wallace,  A.  B 18 

Wiard,  Edward  S 215 

Zinc  Dust 80,  134 

Zinc  Dust  v.  Shaving 80 

Zinc  Shaving 80,  126 


fl|  By  the  use  of  the  Garvin  Method 
the  values  in  your  ore  can  be  re- 
covered in  one-third  the  time,  both 
economically  and  efficiently. 
{J|  The  application  of  this  method  is 
^  not  only  to  gold  and  silver  ores, 
but  all  ores  which  can  be  successfully 
treated  by  wet  process. 
fl|  Why  cling  to  the  old  time  system 
^  of  leaching  or  zinc  precipitation, 
when  you  can  save  one-third  the  time 
by  the  Garvin  Method  and  secure 
better  results? 

{IT  If  you'll  allow  us  an  opportunity, 
^  we'll  prove  the  truth  of  the  above 
claims.  Better  send  for  a  copy  of 
the  Catalog,  anyway. 


Let  us  make  an  actual  working  test  of  your 
ore  to  demonstrate  our  claims  for  this  method. 

400-401    EQUITABLE   BANK    BLDG..    LOS   ANGELES,   CAL. 

Garvin  Cyanide  Extraction  and  Development  Company 

186   MORRISON  ST.,  PORTLAND,  OREGON 

56    WALL   STREET,    NEW    YORK 


An  Ideal  Outfit  for  Refining  Cyanide  Precipitates 

Braun's  "Gary"  Hydrocarbon  Burner 
and  Melting  Furnace 


Gary  Burners  and  Furnaces 

are  made   in   several  sizes. 

Send  for  our  New  Catalog 

"R,"  the  most  comprehensive  book  published  covering 

Metallurgical    Laboratory    Appliances    and    Supplies. 


576-584  Mission   St., 
San  Francisco,   Cal. 


F.W.  BRAUN 


409-415  E.  ThirdlSt., 
Los  Angeles,  Cal. 


STEEL  CYANIDE  TANKS 


CONICAL   BOTTOM    STEEL   TANK 

Work  all  done  with  automatic  machinery  of  our  own 
design.  Perfect  fitting  parts  guaranteed. 

Special  attention  given  to  shipments  for  mule  back 
transportation. 

ESTABLISHED  1872.  35  YEARS'  EXPERIENCE 

WM.  GRAVER  TANK  WORKS 

STEEL  TANKS  AND  PLATE  WORK 

EAST   CHICAGO,    INDIANA 


STORAGE  TANKS 


ALL  SIZES— WRITE  Us 
ALL  PURPOSES 


WARREN    CITY    BOILER    WORKS,    WARREN,    OHIO 


The  Filtration  of  Slime 

by  the  Butters  Method 

{IT  The  BUTTERS  PATENT  VACUUM  FILTER  is  the 
nl  result  of  the  practical  experience  and  investigation  cover- 
ing a  period  of  three  years,  on  a  rebellious  low-grade  tailing 
deposit,  by  Mr.  Charles  Butters  and  associates  at  his  works 
in  Virginia  City,  Nevada. 

The  Butters  Filter  will  positively  increase  the  extraction 
of  the  values  held  in  solutions  of  slow  settling  slime, 
which  can  be  successfully  accomplished  without  the  em- 
ployment of  skilled  labor  to  operate  unnecessary  machinery. 

/TT  The  operation  of  the  Filter  is  continuous,  the  filter- 
nl  leaves  remaining  in  the  boxes  for  months  at  a  time  with- 
out attention  or  disturbance,  thus  eliminating  the  expense 
of  repeated  handling  and  unnecessary  strain  to  the  canvas. 
The  life  of  the  filter-leaves  is  unquestionably  longer  and  the 
practice  cleaner  and  more  efficient. 

An  adoption  of  a  Butters   all-slime  treatment  plant  in 
the  cyanidation  of  your  ore  will  also  permit  of  a  saving 
of  36  per  cent  less  tank  capacitv  required. 

Having  proved   the  usefulness    of  the   Filter  we  solicit 
the   fullest  investigation  of  Mining   Engineers,   Superin- 
tendents, and  Owners  interested  in  cyanide  treatment. 

fWe  are  prepared  to  design  and  superintend  the  installa- 
tion  of    a    complete   plant    for    you    that    will    be    both 
economical  and  productive  of  an  increased  extraction. 

WE  ARE  WORKING  UNDER  VALID  AMERICAN  AND  FOREIGN 
PATENTS  AND  SHALL  PROTECT  OUR  CUSTOMERS 

Attention  is  called  to  the  article  on  'Filtration  of  Slime' 
in  this  volume  by  E.  M.  Hamilton,  for  a  history  of  the 
development  of  the  Butters  method  of  slime  treatment. 

The  Butters  Patent  Vacuum 
Filter  Company,  Inc. 

VIRGINIA  CITY,  NEVADA,  U.  S.  A. 

Apartado  1578,  Mexico  City,  Mexico 


The  Kelly  Patent  Filter  Press 

is  a  self-contained,  self-discharging  tank  pressure  filter, 
which  can  be  operated  by  any  convenient  means  such  as, 
gravity  (where  sufficient  head  is  available),  compressed  air, 
(where  montejus  are  preferred),  or  pumps  of  either  centrifu- 
gal or  plunger  type. 

Filtration  can  be  performed  at  any  required  working  pres- 
sure, up  to  one  hundred  and  twenty-five  pounds. 

Its  chief  points  of  superiority,  which  will  be  appreciated 
by  all  cyanide  mill  operators,  are: 

Absence  of  leakage,  accessibility  of  filter  diaphragms  and 
individual  discharge  of  filtered  solutions  therefrom,  quick 
discharge  of  slime  cakes  in  dry  and  compact  form  affording 
maximum  conservation  of  water  where  this  commodity  is 
scarce,  and  economy  in  operating  cost  as  the  result  of  merely 
nominal  amount  of  manual  labor  involved. 

FOR  FURTHER  INFORMATION,  WRITE  TO 

The  Kelly  Filter  Press  Company  (Jfi^p 

149-151  Pierpont  St.,  Salt  Lake  City,  U.  S.  A. 


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and  Metallurgical  Products 
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